| Message ID | 523195CA.3010305@digi.com |
|---|---|
| State | Changes Requested |
| Headers | show |
Dear Hector Palacios, > Hello, > > Going back to this old thread I have some news regarding the problem with > TFTP transmissions blocking (timed out) after 10 seconds on the FEC of the > MX28. See below: > > On 07/17/2013 05:55 PM, Hector Palacios wrote: > > Dear Marek, > > > > On 07/16/2013 06:44 AM, Marek Vasut wrote: > >> Dear Fabio Estevam, > >> > >>> On Tue, Jul 16, 2013 at 12:51 AM, Fabio Estevam <festevam@gmail.com> wrote: > >>>> On Mon, Jul 15, 2013 at 12:09 PM, Hector Palacios > >>>> > >>>> <hector.palacios@digi.com> wrote: > >>>>> @Fabio: could you manually run the command 'tftp ${loadaddr} > >>>>> file100M' in your EVK? > >>>> > >>>> Yes, this is what I have been running since the beginning. > >>>> > >>>>> If it doesn't fail, could you try running it again after playing with > >>>>> the environment (setting/printing some variables). > >>>> > >>>> I can't reproduce the problem here. > >>>> > >>>>> As I said, this issue appeared with different TFTP servers and is > >>>>> independent of whether the dcache is or not enabled. > >>>> > >>>> Can you transfer from a PC to another PC via TFTP? > > > > Yes I can. > > > >> Another thing of interest would be a 'tcpdump' pcap capture of that > >> connection. > > > > I was initially filtering out only TFTP packets of my wireshark trace and > > all looked correct. After taking a second look to the full trace I see > > now a hint. Around 7 seconds after starting the TFTP transfer the server > > is sending an ARP to the target asking for the owner of the target's IP. > > The target is receiving this ARP and apparently responding (at least > > this is what my debug code shows as it gets into arp.c:ArpReceive(), > > case ARPOP_REQUEST and sending a packet), but this ARP reply from the > > target is not reaching the network. My sniffer does not capture this > > reply. > > > > The server resends the ARP request twice more (seconds 8 and 9) to the > > target and since it doesn't get a reply then sends a broadcast ARP > > (seconds 10) asking who has that IP. Since nobody responds it stops > > sending data. > > > > The times that it works (and I don't know the magic behind using a > > numeric address versus using ${loadaddr} when they have the same value), > > the ARP replies do reach the network and the server continues the > > transmission normally. > > > > Using a v2009 U-Boot, the behaviour is exactly the same, but the target's > > ARP replies always reach the network, and the transfers always succeed. > > > > Since Fabio cannot reproduce it I guess it must be a local ghost. :o( > > We tracked down the issue to an ARP request from the server that was never > answered by the target. We later noticed that the problem did not happen > anymore when building U-Boot with a different toolchain and that the issue > seemed to be in the alignment of the RX buffer in the stack, which old GCC > compilers seem to do wrong. > > Here is a patch: > > From: Robert Hodaszi <robert.hodaszi@digi.com> > Date: Fri, 6 Sep 2013 09:50:52 +0200 > Subject: [PATCH] net: fec: fix invalid temporary RX buffer alignment > because of GCC bug > > Older GCC versions don't handle well alignment on stack variables. > The temporary RX buffer is a local variable, so it is on the stack. > Because the FEC driver is using DMA for transmission, receive and > transmit buffers should be aligned on 64 byte. The transmit buffers are > not allocated in the driver internally, it sends the packets directly > as it gets them. So these packets should be aligned. > When the ARP layer wants to reply to an ARP request, it uses the FEC > driver's temporary RX buffer (used to pass data to the ARP layer) to > store the new packet, and pass it back to the FEC driver's send function. > Because of a GCC bug Can you point to this GCC bug in the GCC bugzilla or something? > this buffer is not aligned well, and when the > driver tries to send it, it first rounds the address down to the > alignment boundary. That causes invalid data. > > To fix it, don't put the temporary onto the stack. > > Signed-off-by: Robert Hodaszi <robert.hodaszi@digi.com> > Signed-off-by: Hector Palacios <hector.palacios@digi.com> > --- > drivers/net/fec_mxc.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c > index f4f72b7..315017e 100644 > --- a/drivers/net/fec_mxc.c > +++ b/drivers/net/fec_mxc.c > @@ -828,7 +828,10 @@ static int fec_recv(struct eth_device *dev) > uint16_t bd_status; > uint32_t addr, size, end; > int i; > - uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); > + /* Don't place this variable on the stack, because older GCC > version + * doesn't handle alignement on stack well. > + */ > + static uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); The buffer might as well be allocated using ALLOC_CACHE_ALIGN_BUFFER() from include/common.h . Still, are you _really_ sure the buffer is unaligned ? Do you have a testcase maybe ? btw. I am able to replicate this issue sometimes even using GCC 4.8.0 . Best regards, Marek Vasut
Dear Robert Hodaszi, > <html> > <head> > <meta content="text/html; charset=ISO-8859-1" > http-equiv="Content-Type"> > </head> > <body bgcolor="#FFFFFF" text="#000000"> > <div class="moz-cite-prefix">Hi,<br> > <br> > There are a lot of bug announcement, just make a search:<br> > <meta http-equiv="content-type" content="text/html; > charset=ISO-8859-1"> > <a > href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33721">http://gcc.gnu.or > g/bugzilla/show_bug.cgi?id=33721</a><br> <meta http-equiv="content-type" > content="text/html; > charset=ISO-8859-1"> > <a > href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16660">http://gcc.gnu.or > g/bugzilla/show_bug.cgi?id=16660</a><br> <br> > Also, I printed out the buffer addresses, and that temporary RX > buffer was not aligned. So the transmit function rounded it down > to the alignment boundary, and so caused invalid data > transmission. (By the way. Shouldn't the transmit function check > whether the alignment is proper, and throw an error message, > instead of round it down? That would make more sense.)<br> > <div class="moz-signature"><br> > Best regards,<br> > Robert Hodaszi > </div> > <br> > On 2013-09-12 12:50, Marek Vasut wrote:<br> > </div> > <blockquote cite="mid:201309121250.36579.marex@denx.de" type="cite"> > <pre wrap="">Dear Hector Palacios, [...] Sorry, I cannot decode this. Can you please send plain-text emails? Thank you Best regards, Marek Vasut
Hi, Sorry, hopefully that will be a plain-text. There are a lot of bug announcement, just make a search: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33721 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16660 Also, I printed out the buffer addresses, and that temporary RX buffer was not aligned. So the transmit function rounded it down to the alignment boundary, and so caused invalid data transmission. (By the way. Shouldn't the transmit function check whether the alignment is proper, and throw an error message, instead of round it down? That would make more sense.) Best regards, Robert Hodaszi On 2013-09-12 12:50, Marek Vasut wrote: > Dear Hector Palacios, > >> Hello, >> >> Going back to this old thread I have some news regarding the problem with >> TFTP transmissions blocking (timed out) after 10 seconds on the FEC of the >> MX28. See below: >> >> On 07/17/2013 05:55 PM, Hector Palacios wrote: >>> Dear Marek, >>> >>> On 07/16/2013 06:44 AM, Marek Vasut wrote: >>>> Dear Fabio Estevam, >>>> >>>>> On Tue, Jul 16, 2013 at 12:51 AM, Fabio Estevam<festevam@gmail.com> > wrote: >>>>>> On Mon, Jul 15, 2013 at 12:09 PM, Hector Palacios >>>>>> >>>>>> <hector.palacios@digi.com> wrote: >>>>>>> @Fabio: could you manually run the command 'tftp ${loadaddr} >>>>>>> file100M' in your EVK? >>>>>> Yes, this is what I have been running since the beginning. >>>>>> >>>>>>> If it doesn't fail, could you try running it again after playing with >>>>>>> the environment (setting/printing some variables). >>>>>> I can't reproduce the problem here. >>>>>> >>>>>>> As I said, this issue appeared with different TFTP servers and is >>>>>>> independent of whether the dcache is or not enabled. >>>>>> Can you transfer from a PC to another PC via TFTP? >>> Yes I can. >>> >>>> Another thing of interest would be a 'tcpdump' pcap capture of that >>>> connection. >>> I was initially filtering out only TFTP packets of my wireshark trace and >>> all looked correct. After taking a second look to the full trace I see >>> now a hint. Around 7 seconds after starting the TFTP transfer the server >>> is sending an ARP to the target asking for the owner of the target's IP. >>> The target is receiving this ARP and apparently responding (at least >>> this is what my debug code shows as it gets into arp.c:ArpReceive(), >>> case ARPOP_REQUEST and sending a packet), but this ARP reply from the >>> target is not reaching the network. My sniffer does not capture this >>> reply. >>> >>> The server resends the ARP request twice more (seconds 8 and 9) to the >>> target and since it doesn't get a reply then sends a broadcast ARP >>> (seconds 10) asking who has that IP. Since nobody responds it stops >>> sending data. >>> >>> The times that it works (and I don't know the magic behind using a >>> numeric address versus using ${loadaddr} when they have the same value), >>> the ARP replies do reach the network and the server continues the >>> transmission normally. >>> >>> Using a v2009 U-Boot, the behaviour is exactly the same, but the target's >>> ARP replies always reach the network, and the transfers always succeed. >>> >>> Since Fabio cannot reproduce it I guess it must be a local ghost. :o( >> We tracked down the issue to an ARP request from the server that was never >> answered by the target. We later noticed that the problem did not happen >> anymore when building U-Boot with a different toolchain and that the issue >> seemed to be in the alignment of the RX buffer in the stack, which old GCC >> compilers seem to do wrong. >> >> Here is a patch: >> >> From: Robert Hodaszi<robert.hodaszi@digi.com> >> Date: Fri, 6 Sep 2013 09:50:52 +0200 >> Subject: [PATCH] net: fec: fix invalid temporary RX buffer alignment >> because of GCC bug >> >> Older GCC versions don't handle well alignment on stack variables. >> The temporary RX buffer is a local variable, so it is on the stack. >> Because the FEC driver is using DMA for transmission, receive and >> transmit buffers should be aligned on 64 byte. The transmit buffers are >> not allocated in the driver internally, it sends the packets directly >> as it gets them. So these packets should be aligned. >> When the ARP layer wants to reply to an ARP request, it uses the FEC >> driver's temporary RX buffer (used to pass data to the ARP layer) to >> store the new packet, and pass it back to the FEC driver's send function. >> Because of a GCC bug > Can you point to this GCC bug in the GCC bugzilla or something? > >> this buffer is not aligned well, and when the >> driver tries to send it, it first rounds the address down to the >> alignment boundary. That causes invalid data. >> >> To fix it, don't put the temporary onto the stack. >> >> Signed-off-by: Robert Hodaszi<robert.hodaszi@digi.com> >> Signed-off-by: Hector Palacios<hector.palacios@digi.com> >> --- >> drivers/net/fec_mxc.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c >> index f4f72b7..315017e 100644 >> --- a/drivers/net/fec_mxc.c >> +++ b/drivers/net/fec_mxc.c >> @@ -828,7 +828,10 @@ static int fec_recv(struct eth_device *dev) >> uint16_t bd_status; >> uint32_t addr, size, end; >> int i; >> - uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); >> + /* Don't place this variable on the stack, because older GCC >> version + * doesn't handle alignement on stack well. >> + */ >> + static uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); > The buffer might as well be allocated using ALLOC_CACHE_ALIGN_BUFFER() from > include/common.h . Still, are you _really_ sure the buffer is unaligned ? Do you > have a testcase maybe ? > > btw. I am able to replicate this issue sometimes even using GCC 4.8.0 . > > Best regards, > Marek Vasut
Hi, Sorry, hopefully that will be a plain-text. There are a lot of bug announcement, just make a search: gcc.gnu.org/bugzilla/show_bug.cgi?id=33721 gcc.gnu.org/bugzilla/show_bug.cgi?id=16660 Also, I printed out the buffer addresses, and that temporary RX buffer was not aligned. So the transmit function rounded it down to the alignment boundary, and so caused invalid data transmission. (By the way. Shouldn't the transmit function check whether the alignment is proper, and throw an error message, instead of round it down? That would make more sense.) Best regards, Robert Hodaszi On 2013-09-12 12:50, Marek Vasut wrote: > Dear Hector Palacios, > >> Hello, >> >> Going back to this old thread I have some news regarding the problem with >> TFTP transmissions blocking (timed out) after 10 seconds on the FEC of the >> MX28. See below: >> >> On 07/17/2013 05:55 PM, Hector Palacios wrote: >>> Dear Marek, >>> >>> On 07/16/2013 06:44 AM, Marek Vasut wrote: >>>> Dear Fabio Estevam, >>>> >>>>> On Tue, Jul 16, 2013 at 12:51 AM, Fabio Estevam<festevam@gmail.com> > wrote: >>>>>> On Mon, Jul 15, 2013 at 12:09 PM, Hector Palacios >>>>>> >>>>>> <hector.palacios@digi.com> wrote: >>>>>>> @Fabio: could you manually run the command 'tftp ${loadaddr} >>>>>>> file100M' in your EVK? >>>>>> Yes, this is what I have been running since the beginning. >>>>>> >>>>>>> If it doesn't fail, could you try running it again after playing with >>>>>>> the environment (setting/printing some variables). >>>>>> I can't reproduce the problem here. >>>>>> >>>>>>> As I said, this issue appeared with different TFTP servers and is >>>>>>> independent of whether the dcache is or not enabled. >>>>>> Can you transfer from a PC to another PC via TFTP? >>> Yes I can. >>> >>>> Another thing of interest would be a 'tcpdump' pcap capture of that >>>> connection. >>> I was initially filtering out only TFTP packets of my wireshark trace and >>> all looked correct. After taking a second look to the full trace I see >>> now a hint. Around 7 seconds after starting the TFTP transfer the server >>> is sending an ARP to the target asking for the owner of the target's IP. >>> The target is receiving this ARP and apparently responding (at least >>> this is what my debug code shows as it gets into arp.c:ArpReceive(), >>> case ARPOP_REQUEST and sending a packet), but this ARP reply from the >>> target is not reaching the network. My sniffer does not capture this >>> reply. >>> >>> The server resends the ARP request twice more (seconds 8 and 9) to the >>> target and since it doesn't get a reply then sends a broadcast ARP >>> (seconds 10) asking who has that IP. Since nobody responds it stops >>> sending data. >>> >>> The times that it works (and I don't know the magic behind using a >>> numeric address versus using ${loadaddr} when they have the same value), >>> the ARP replies do reach the network and the server continues the >>> transmission normally. >>> >>> Using a v2009 U-Boot, the behaviour is exactly the same, but the target's >>> ARP replies always reach the network, and the transfers always succeed. >>> >>> Since Fabio cannot reproduce it I guess it must be a local ghost. :o( >> We tracked down the issue to an ARP request from the server that was never >> answered by the target. We later noticed that the problem did not happen >> anymore when building U-Boot with a different toolchain and that the issue >> seemed to be in the alignment of the RX buffer in the stack, which old GCC >> compilers seem to do wrong. >> >> Here is a patch: >> >> From: Robert Hodaszi<robert.hodaszi@digi.com> >> Date: Fri, 6 Sep 2013 09:50:52 +0200 >> Subject: [PATCH] net: fec: fix invalid temporary RX buffer alignment >> because of GCC bug >> >> Older GCC versions don't handle well alignment on stack variables. >> The temporary RX buffer is a local variable, so it is on the stack. >> Because the FEC driver is using DMA for transmission, receive and >> transmit buffers should be aligned on 64 byte. The transmit buffers are >> not allocated in the driver internally, it sends the packets directly >> as it gets them. So these packets should be aligned. >> When the ARP layer wants to reply to an ARP request, it uses the FEC >> driver's temporary RX buffer (used to pass data to the ARP layer) to >> store the new packet, and pass it back to the FEC driver's send function. >> Because of a GCC bug > Can you point to this GCC bug in the GCC bugzilla or something? > >> this buffer is not aligned well, and when the >> driver tries to send it, it first rounds the address down to the >> alignment boundary. That causes invalid data. >> >> To fix it, don't put the temporary onto the stack. >> >> Signed-off-by: Robert Hodaszi<robert.hodaszi@digi.com> >> Signed-off-by: Hector Palacios<hector.palacios@digi.com> >> --- >> drivers/net/fec_mxc.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c >> index f4f72b7..315017e 100644 >> --- a/drivers/net/fec_mxc.c >> +++ b/drivers/net/fec_mxc.c >> @@ -828,7 +828,10 @@ static int fec_recv(struct eth_device *dev) >> uint16_t bd_status; >> uint32_t addr, size, end; >> int i; >> - uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); >> + /* Don't place this variable on the stack, because older GCC >> version + * doesn't handle alignement on stack well. >> + */ >> + static uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); > The buffer might as well be allocated using ALLOC_CACHE_ALIGN_BUFFER() from > include/common.h . Still, are you _really_ sure the buffer is unaligned ? Do you > have a testcase maybe ? > > btw. I am able to replicate this issue sometimes even using GCC 4.8.0 . > > Best regards, > Marek Vasut
Dear Robert Hodaszi, > Hi, > > Sorry, hopefully that will be a plain-text. > > There are a lot of bug announcement, just make a search: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33721 This was apparently fixed three years ago. > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16660 And this one six years ago ... > Also, I printed out the buffer addresses, and that temporary RX buffer > was not aligned. So the transmit function rounded it down to the > alignment boundary, and so caused invalid data transmission. (By the > way. Shouldn't the transmit function check whether the alignment is > proper, and throw an error message, instead of round it down? That would > make more sense.) Looking at the code one more time, it'd make most sense to simply allocate the buffer NOT on stack, but with some memalign-kind-of call to avoid this abuse of stack. You see, the max packet size is around 2k, which is quite a lot. How does this proposal sound to you ? Best regards, Marek Vasut
I just brought up two samples, that it was a long-term problem. Now it is fixed. But if somebody is trying to compile the U-Boot with an older toolchain, it could cause problems. I had problems with 4.4.6. Yes, 2k is a lot, and I would not put it on the stack. That was just a quick fix. It would be nicer to allocate the memory with malloc, and should do that at initialization time. Best regards, Robert Hodaszi On 2013-09-12 16:05, Marek Vasut wrote: > Dear Robert Hodaszi, > >> Hi, >> >> Sorry, hopefully that will be a plain-text. >> >> There are a lot of bug announcement, just make a search: >> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33721 > This was apparently fixed three years ago. > >> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16660 > And this one six years ago ... > >> Also, I printed out the buffer addresses, and that temporary RX buffer >> was not aligned. So the transmit function rounded it down to the >> alignment boundary, and so caused invalid data transmission. (By the >> way. Shouldn't the transmit function check whether the alignment is >> proper, and throw an error message, instead of round it down? That would >> make more sense.) > Looking at the code one more time, it'd make most sense to simply allocate the > buffer NOT on stack, but with some memalign-kind-of call to avoid this abuse of > stack. You see, the max packet size is around 2k, which is quite a lot. How does > this proposal sound to you ? > > Best regards, > Marek Vasut
Dear Robert Hodaszi, > I just brought up two samples, that it was a long-term problem. Now it > is fixed. But if somebody is trying to compile the U-Boot with an older > toolchain, it could cause problems. I had problems with 4.4.6. > > Yes, 2k is a lot, and I would not put it on the stack. That was just a > quick fix. It would be nicer to allocate the memory with malloc, and > should do that at initialization time. Please do not top-post. Memalign should do here with proper rounding. Can you prepare another patch please? Best regards, Marek Vasut
On 2013-09-12 16:31, Marek Vasut wrote: > Dear Robert Hodaszi, > > Please do not top-post. > > Memalign should do here with proper rounding. Can you prepare another patch > please? > > Best regards, > Marek Vasut Ok. I will try to do that tomorrow. Best regards, Robert Hodaszi
Dear Robert Hodaszi, > On 2013-09-12 16:31, Marek Vasut wrote: > > Dear Robert Hodaszi, > > > > Please do not top-post. > > > > Memalign should do here with proper rounding. Can you prepare another > > patch please? > > > > Best regards, > > Marek Vasut > > Ok. I will try to do that tomorrow. Cool, thanks ! Nice find btw ;-) Best regards, Marek Vasut
Dear Hector Palacios, In message <523195CA.3010305@digi.com> you wrote: > > Here is a patch: > > From: Robert Hodaszi <robert.hodaszi@digi.com> > Date: Fri, 6 Sep 2013 09:50:52 +0200 > Subject: [PATCH] net: fec: fix invalid temporary RX buffer alignment because > of GCC bug > > Older GCC versions don't handle well alignment on stack variables. Can you please be specific - which exact versions of GCC are supposed to misbehave here? > To fix it, don't put the temporary onto the stack. This is not a good idea, as it wastes a memory for no good reason. > Signed-off-by: Robert Hodaszi <robert.hodaszi@digi.com> > Signed-off-by: Hector Palacios <hector.palacios@digi.com> > --- > drivers/net/fec_mxc.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c > index f4f72b7..315017e 100644 > --- a/drivers/net/fec_mxc.c > +++ b/drivers/net/fec_mxc.c > @@ -828,7 +828,10 @@ static int fec_recv(struct eth_device *dev) > uint16_t bd_status; > uint32_t addr, size, end; > int i; > - uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); > + /* Don't place this variable on the stack, because older GCC version > + * doesn't handle alignement on stack well. > + */ > + static uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); I have to admit that I doubt the explanation - somthing else is probaly wrong instead. I would really like to know which compiler version misbehaves, and what the generated code looks like, both in the working and in the broken case. Thanks. Best regards, Wolfgang Denk
Dear Robert Hodaszi, In message <5231A0C0.8070308@digi.com> you wrote: > > Sorry, hopefully that will be a plain-text. > > There are a lot of bug announcement, just make a search: > gcc.gnu.org/bugzilla/show_bug.cgi?id=33721 > gcc.gnu.org/bugzilla/show_bug.cgi?id=16660 Hm... what exactly are the values of STACK_BOUNDARY and PREFERRED_STACK_BOUNDARY for the failing version of GCC, then? Best regards, Wolfgang Denk
Dear Marek Vasut, In message <201309121605.04824.marex@denx.de> you wrote: > > Looking at the code one more time, it'd make most sense to simply allocate the > buffer NOT on stack, but with some memalign-kind-of call to avoid this abuse of > stack. You see, the max packet size is around 2k, which is quite a lot. How does > this proposal sound to you ? It makes perfect sense to allocate variable with function scope only on the stack. That's what the stack has been invented for. If there is a bug with that, this mug must be isolated and fixed. It makes zero sense to just paper over it. Best regards, Wolfgang Denk
On Thu, Sep 12, 2013 at 3:17 PM, Wolfgang Denk <wd@denx.de> wrote: > Dear Marek Vasut, > > In message <201309121605.04824.marex@denx.de> you wrote: >> >> Looking at the code one more time, it'd make most sense to simply allocate the >> buffer NOT on stack, but with some memalign-kind-of call to avoid this abuse of >> stack. You see, the max packet size is around 2k, which is quite a lot. How does >> this proposal sound to you ? > > It makes perfect sense to allocate variable with function scope only > on the stack. That's what the stack has been invented for. This buffer in the fec driver will be used in DMA transfer, so maybe that's the reason we should use malloc instead of using the stack? At least in the kernel, we don't use stack for DMA buffers.
Dear Fabio Estevam, In message <CAOMZO5BY6kDOCoWn_SRwhPE7ssMjAReZ2bcFXGgFF-_Wrdgo0g@mail.gmail.com> you wrote: > > > It makes perfect sense to allocate variable with function scope only > > on the stack. That's what the stack has been invented for. > > This buffer in the fec driver will be used in DMA transfer, so maybe > that's the reason we should use malloc instead of using the stack? What has DMA to do with that? We're talking about alignment only. > At least in the kernel, we don't use stack for DMA buffers. Yes, but them, the kernel uses a much more complicated memory setup, with somewhat different mappings for different regions. We don't do that - or do we? IMO we use a single mapping for the whole RAM ? Best regards, Wolfgang Denk
On Thu, Sep 12, 2013 at 3:53 PM, Wolfgang Denk <wd@denx.de> wrote: > Dear Fabio Estevam, > > In message <CAOMZO5BY6kDOCoWn_SRwhPE7ssMjAReZ2bcFXGgFF-_Wrdgo0g@mail.gmail.com> you wrote: >> >> > It makes perfect sense to allocate variable with function scope only >> > on the stack. That's what the stack has been invented for. >> >> This buffer in the fec driver will be used in DMA transfer, so maybe >> that's the reason we should use malloc instead of using the stack? > > What has DMA to do with that? We're talking about alignment only. I mentioned DMA because we align the buffer with __aligned(ARCH_DMA_MINALIGN). Will try to see if I can reproduce the problem here, but the last time I tried I was not able to. Maybe the gcc version that Robert and Hector pointed out may explain the different behaviour. Regards, Fabio Estevam
diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c index f4f72b7..315017e 100644 --- a/drivers/net/fec_mxc.c +++ b/drivers/net/fec_mxc.c @@ -828,7 +828,10 @@ static int fec_recv(struct eth_device *dev) uint16_t bd_status; uint32_t addr, size, end; int i; - uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); + /* Don't place this variable on the stack, because older GCC version + * doesn't handle alignement on stack well. + */ + static uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN); /* * Check if any critical events have happened