| Message ID | 20170517053908.26138-4-chris.packham@alliedtelesis.co.nz |
|---|---|
| State | Superseded |
| Headers | show |
On Wed, May 17, 2017 at 05:39:07PM +1200, Chris Packham wrote: > Setting the of_node for the mtd device allows the generic mtd code to > setup the partitions. Additionally we must specify a non-zero erasesize > for the partitions to be writeable. > > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> Reviewed-by: Andrew Lunn <andrew@lunn.ch> Andrew
Hi Chris, On Wed, 17 May 2017 17:39:07 +1200 Chris Packham <chris.packham@alliedtelesis.co.nz> wrote: > Setting the of_node for the mtd device allows the generic mtd code to > setup the partitions. Additionally we must specify a non-zero erasesize > for the partitions to be writeable. > > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> > --- > drivers/mtd/devices/mchp23k256.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c > index 2542f5b8b63f..02c6b9dcbd3e 100644 > --- a/drivers/mtd/devices/mchp23k256.c > +++ b/drivers/mtd/devices/mchp23k256.c > @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi) > > data = dev_get_platdata(&spi->dev); > > + mtd_set_of_node(&flash->mtd, spi->dev.of_node); > flash->mtd.dev.parent = &spi->dev; > flash->mtd.type = MTD_RAM; > flash->mtd.flags = MTD_CAP_RAM; > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) > flash->mtd._read = mchp23k256_read; > flash->mtd._write = mchp23k256_write; > > + flash->mtd.erasesize = PAGE_SIZE; > + while (flash->mtd.size & (flash->mtd.erasesize - 1)) > + flash->mtd.erasesize >>= 1; > + Can we fix allocate_partition() to properly handle the master->erasesize == 0 case instead of doing that? Thanks, Boris
On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: > Hi Chris, > > On Wed, 17 May 2017 17:39:07 +1200 > Chris Packham <chris.packham@alliedtelesis.co.nz> wrote: > > > Setting the of_node for the mtd device allows the generic mtd code to > > setup the partitions. Additionally we must specify a non-zero erasesize > > for the partitions to be writeable. > > > > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> > > --- > > drivers/mtd/devices/mchp23k256.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c > > index 2542f5b8b63f..02c6b9dcbd3e 100644 > > --- a/drivers/mtd/devices/mchp23k256.c > > +++ b/drivers/mtd/devices/mchp23k256.c > > @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi) > > > > data = dev_get_platdata(&spi->dev); > > > > + mtd_set_of_node(&flash->mtd, spi->dev.of_node); > > flash->mtd.dev.parent = &spi->dev; > > flash->mtd.type = MTD_RAM; > > flash->mtd.flags = MTD_CAP_RAM; > > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) > > flash->mtd._read = mchp23k256_read; > > flash->mtd._write = mchp23k256_write; > > > > + flash->mtd.erasesize = PAGE_SIZE; > > + while (flash->mtd.size & (flash->mtd.erasesize - 1)) > > + flash->mtd.erasesize >>= 1; > > + > > Can we fix allocate_partition() to properly handle the > master->erasesize == 0 case instead of doing that? Is everything actually ready for the eraseblock size to be 0? That would seem surprising to many applications, I would think. Can you, for instance, even use UBI on such a device? BTW, I feel like this check is a little more natural to do with 'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently meaningless) erasesize. (I realize there's a later version of these patches, but I figured I'd put my comments where the suggestion was brought up.) Brian
Le Thu, 1 Jun 2017 11:43:40 -0700, Brian Norris <computersforpeace@gmail.com> a écrit : > On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: > > Hi Chris, > > > > On Wed, 17 May 2017 17:39:07 +1200 > > Chris Packham <chris.packham@alliedtelesis.co.nz> wrote: > > > > > Setting the of_node for the mtd device allows the generic mtd code to > > > setup the partitions. Additionally we must specify a non-zero erasesize > > > for the partitions to be writeable. > > > > > > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> > > > --- > > > drivers/mtd/devices/mchp23k256.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c > > > index 2542f5b8b63f..02c6b9dcbd3e 100644 > > > --- a/drivers/mtd/devices/mchp23k256.c > > > +++ b/drivers/mtd/devices/mchp23k256.c > > > @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi) > > > > > > data = dev_get_platdata(&spi->dev); > > > > > > + mtd_set_of_node(&flash->mtd, spi->dev.of_node); > > > flash->mtd.dev.parent = &spi->dev; > > > flash->mtd.type = MTD_RAM; > > > flash->mtd.flags = MTD_CAP_RAM; > > > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) > > > flash->mtd._read = mchp23k256_read; > > > flash->mtd._write = mchp23k256_write; > > > > > > + flash->mtd.erasesize = PAGE_SIZE; > > > + while (flash->mtd.size & (flash->mtd.erasesize - 1)) > > > + flash->mtd.erasesize >>= 1; > > > + > > > > Can we fix allocate_partition() to properly handle the > > master->erasesize == 0 case instead of doing that? > > Is everything actually ready for the eraseblock size to be 0? That would > seem surprising to many applications, I would think. Can you, for > instance, even use UBI on such a device? Well, I think it's already broken. AFAICT this driver does not implement ->_erase(), and mtd_erase() does not check if MTD_NO_ERASE is set before calling mtd->_erase(), neither UBI does before calling mtd_erase(). Between a NULL pointer exception and a div-by-zero exception, I can't decide what is better :-). IMO, we'd better add a check in UBI to refuse to attach a device with MTD_NO_ERASE or mtd->erasesize == 0, and fix other places that don't check erasesize value instead of putting a fake erasesize and using a dummy ->_erase() implementation for those devices that simply can't be erased. We should also probably complain with -ENOTSUPP when someone calls mtd_erase() on a device with MTD_NO_ERASE and add more checks in the add_mtd_device() to detect drivers that don't have MTD_NO_ERASE set and do not implement ->_erase() or leave ->erasesize to 0. > > BTW, I feel like this check is a little more natural to do with > 'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently > meaningless) erasesize. Fair enough.
On 02/06/17 06:43, Brian Norris wrote: > On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: >> Hi Chris, >> >> On Wed, 17 May 2017 17:39:07 +1200 >> Chris Packham <chris.packham@alliedtelesis.co.nz> wrote: >> >>> Setting the of_node for the mtd device allows the generic mtd code to >>> setup the partitions. Additionally we must specify a non-zero erasesize >>> for the partitions to be writeable. >>> >>> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> >>> --- >>> drivers/mtd/devices/mchp23k256.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c >>> index 2542f5b8b63f..02c6b9dcbd3e 100644 >>> --- a/drivers/mtd/devices/mchp23k256.c >>> +++ b/drivers/mtd/devices/mchp23k256.c >>> @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi) >>> >>> data = dev_get_platdata(&spi->dev); >>> >>> + mtd_set_of_node(&flash->mtd, spi->dev.of_node); >>> flash->mtd.dev.parent = &spi->dev; >>> flash->mtd.type = MTD_RAM; >>> flash->mtd.flags = MTD_CAP_RAM; >>> @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) >>> flash->mtd._read = mchp23k256_read; >>> flash->mtd._write = mchp23k256_write; >>> >>> + flash->mtd.erasesize = PAGE_SIZE; >>> + while (flash->mtd.size & (flash->mtd.erasesize - 1)) >>> + flash->mtd.erasesize >>= 1; >>> + >> >> Can we fix allocate_partition() to properly handle the >> master->erasesize == 0 case instead of doing that? > > Is everything actually ready for the eraseblock size to be 0? That was my initial motivation for faking it. > That would > seem surprising to many applications, I would think. Can you, for > instance, even use UBI on such a device? I've tried ext2 and I believe Andrew has tried minix fs. We're talking SRAM so UBI/UBIFS doesn't really provide much benefit for this use-case. > BTW, I feel like this check is a little more natural to do with > 'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently > meaningless) erasesize. > > (I realize there's a later version of these patches, but I figured I'd > put my comments where the suggestion was brought up.) > > Brian >
On Thu, Jun 01, 2017 at 10:47:12PM +0200, Boris Brezillon wrote: > Le Thu, 1 Jun 2017 11:43:40 -0700, > Brian Norris <computersforpeace@gmail.com> a écrit : > > On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: > > > On Wed, 17 May 2017 17:39:07 +1200 > > > Chris Packham <chris.packham@alliedtelesis.co.nz> wrote: > > > > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) > > > > flash->mtd._read = mchp23k256_read; > > > > flash->mtd._write = mchp23k256_write; > > > > > > > > + flash->mtd.erasesize = PAGE_SIZE; > > > > + while (flash->mtd.size & (flash->mtd.erasesize - 1)) > > > > + flash->mtd.erasesize >>= 1; > > > > + > > > > > > Can we fix allocate_partition() to properly handle the > > > master->erasesize == 0 case instead of doing that? > > > > Is everything actually ready for the eraseblock size to be 0? That would > > seem surprising to many applications, I would think. Can you, for > > instance, even use UBI on such a device? > > Well, I think it's already broken. AFAICT this driver does not > implement ->_erase(), and mtd_erase() does not check if MTD_NO_ERASE is > set before calling mtd->_erase(), neither UBI does before calling > mtd_erase(). Sure. > Between a NULL pointer exception and a div-by-zero exception, I can't > decide what is better :-). Well, there are other potential problems than that. What if someone was iterating over the device size, by increments of erasesize? Infinite loop! Or what about anything that might have assumed 'writesize < erasesize'? I'm mostly thinking out loud, because I'm not sure there's a really good way to handle this, other than stop making those assumptions. (A *possible* solution would be to have MTD enforce a fake erasesize for NO_ERASE flash, instead of making drivers do it, like Chris was trying. But I'm not sure that's a good one.) > IMO, we'd better add a check in UBI to refuse to attach a device with > MTD_NO_ERASE or mtd->erasesize == 0, and fix other places that don't > check erasesize value instead of putting a fake erasesize and using a > dummy ->_erase() implementation for those devices that simply can't be > erased. That's probably a good idea. > We should also probably complain with -ENOTSUPP when someone calls > mtd_erase() on a device with MTD_NO_ERASE and add more checks in the > add_mtd_device() to detect drivers that don't have MTD_NO_ERASE set > and do not implement ->_erase() or leave ->erasesize to 0. Yep. > > BTW, I feel like this check is a little more natural to do with > > 'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently > > meaningless) erasesize. > > Fair enough. OK, well I'll take another look at v4, but that might be my only criticism then. Overall though, a "NO_ERASE" MTD makes me wonder why it's an MTD in the first place. I guess we're kinda the wild west of things that don't fit into the block subsystem... Brian
On Thu, Jun 01, 2017 at 09:30:07PM +0000, Chris Packham wrote: > On 02/06/17 06:43, Brian Norris wrote: > > On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: > >> Can we fix allocate_partition() to properly handle the > >> master->erasesize == 0 case instead of doing that? > > > > Is everything actually ready for the eraseblock size to be 0? > > That was my initial motivation for faking it. Understood. I think it's probably better to avoid hacking drivers like you were about to, but I was also curious if anyone had thought through the implications of *not* forcing a non-zero size. > > That would > > seem surprising to many applications, I would think. Can you, for > > instance, even use UBI on such a device? > > I've tried ext2 and I believe Andrew has tried minix fs. We're talking > SRAM so UBI/UBIFS doesn't really provide much benefit for this use-case. Right. But that's not necessarily true for all NO_ERASE devices, so we'd probably want to think about that before allowing it. Brian
On 02/06/17 10:23, Brian Norris wrote: > On Thu, Jun 01, 2017 at 09:30:07PM +0000, Chris Packham wrote: >> On 02/06/17 06:43, Brian Norris wrote: >>> On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: >>>> Can we fix allocate_partition() to properly handle the >>>> master->erasesize == 0 case instead of doing that? >>> >>> Is everything actually ready for the eraseblock size to be 0? >> >> That was my initial motivation for faking it. > > Understood. I think it's probably better to avoid hacking drivers like > you were about to, but I was also curious if anyone had thought through > the implications of *not* forcing a non-zero size. > >>> That would >>> seem surprising to many applications, I would think. Can you, for >>> instance, even use UBI on such a device? >> >> I've tried ext2 and I believe Andrew has tried minix fs. We're talking >> SRAM so UBI/UBIFS doesn't really provide much benefit for this use-case. > > Right. But that's not necessarily true for all NO_ERASE devices, so we'd > probably want to think about that before allowing it. Do we need a flag to indicate SRAM-like properties? I assume there is a difference between NO_ERASE on ROM devices where there is just no way of erasing the data. For {S,F,M}RAM there is no block erase operation but you can overwrite data to destroy it (which is actually my use-case with this SPI SRAM). I was tempted to set erase_size = 1 at one point which in my mind was technically accurate but would probably upset the mtd layer just as much as 0.
On Thu, 1 Jun 2017 15:01:56 -0700 Brian Norris <computersforpeace@gmail.com> wrote: > On Thu, Jun 01, 2017 at 10:47:12PM +0200, Boris Brezillon wrote: > > Le Thu, 1 Jun 2017 11:43:40 -0700, > > Brian Norris <computersforpeace@gmail.com> a écrit : > > > On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: > > > > On Wed, 17 May 2017 17:39:07 +1200 > > > > Chris Packham <chris.packham@alliedtelesis.co.nz> wrote: > > > > > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) > > > > > flash->mtd._read = mchp23k256_read; > > > > > flash->mtd._write = mchp23k256_write; > > > > > > > > > > + flash->mtd.erasesize = PAGE_SIZE; > > > > > + while (flash->mtd.size & (flash->mtd.erasesize - 1)) > > > > > + flash->mtd.erasesize >>= 1; > > > > > + > > > > > > > > Can we fix allocate_partition() to properly handle the > > > > master->erasesize == 0 case instead of doing that? > > > > > > Is everything actually ready for the eraseblock size to be 0? That would > > > seem surprising to many applications, I would think. Can you, for > > > instance, even use UBI on such a device? > > > > Well, I think it's already broken. AFAICT this driver does not > > implement ->_erase(), and mtd_erase() does not check if MTD_NO_ERASE is > > set before calling mtd->_erase(), neither UBI does before calling > > mtd_erase(). > > Sure. > > > Between a NULL pointer exception and a div-by-zero exception, I can't > > decide what is better :-). > > Well, there are other potential problems than that. What if someone was > iterating over the device size, by increments of erasesize? Infinite > loop! Or what about anything that might have assumed > 'writesize < erasesize'? Absolutely, div-by-zero is not the only problem we can face. > > I'm mostly thinking out loud, because I'm not sure there's a really good > way to handle this, other than stop making those assumptions. > > (A *possible* solution would be to have MTD enforce a fake erasesize for > NO_ERASE flash, instead of making drivers do it, like Chris was trying. > But I'm not sure that's a good one.) Actually, by doing that we keep encouraging people to not do the right thing :-). > > > IMO, we'd better add a check in UBI to refuse to attach a device with > > MTD_NO_ERASE or mtd->erasesize == 0, and fix other places that don't > > check erasesize value instead of putting a fake erasesize and using a > > dummy ->_erase() implementation for those devices that simply can't be > > erased. > > That's probably a good idea. I'll try to post patches soon, but they definitely won't fix all problems. For example, we just can't catch the infinite loop issue you are mentioning above. > > > We should also probably complain with -ENOTSUPP when someone calls > > mtd_erase() on a device with MTD_NO_ERASE and add more checks in the > > add_mtd_device() to detect drivers that don't have MTD_NO_ERASE set > > and do not implement ->_erase() or leave ->erasesize to 0. > > Yep. > > > > BTW, I feel like this check is a little more natural to do with > > > 'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently > > > meaningless) erasesize. > > > > Fair enough. > > OK, well I'll take another look at v4, but that might be my only > criticism then. > > Overall though, a "NO_ERASE" MTD makes me wonder why it's an MTD in the > first place. I guess we're kinda the wild west of things that don't fit > into the block subsystem... Yes, that's exactly what the MTD subsystem is: a place where you can put drivers for memory devices that are not block devices :-). Don't know if it's a good thing or not, but it definitely makes MTD users life harder. BTW, MTD_NO_ERASE is not the only problem we have with UBI or JFFS2. Are we guaranteed that an erase operation fills an eraseblock with ones? Don't we have mem technologies that are filling them with zeros? Note that mtdram is artificially setting the mem-region to 0xff in its dummy erase operation, so maybe it's a implicit rule that ->_erase() is supposed to fill eraseblocks with 0xff.
On Thu, Jun 01, 2017 at 11:08:08PM +0000, Chris Packham wrote: > Do we need a flag to indicate SRAM-like properties? I assume there is a > difference between NO_ERASE on ROM devices where there is just no way of > erasing the data. For {S,F,M}RAM there is no block erase operation but I think we already have that: #define MTD_CAP_ROM 0 #define MTD_CAP_RAM (MTD_WRITEABLE | MTD_BIT_WRITEABLE | MTD_NO_ERASE) The key signifier for ROM would be !MTD_WRITEABLE. > you can overwrite data to destroy it (which is actually my use-case with > this SPI SRAM). I was tempted to set erase_size = 1 at one point which > in my mind was technically accurate but would probably upset the mtd > layer just as much as 0. I'm not sure what erasesize should be here. I suppose 0, but really, I think the MTD_NO_ERASE flag is the clearer indication that erase is not needed, and that one should ignore the erasesize. Brian
On Fri, Jun 02, 2017 at 11:04:06AM +0200, Boris Brezillon wrote: > BTW, MTD_NO_ERASE is not the only problem we have with UBI or JFFS2. > Are we guaranteed that an erase operation fills an eraseblock with > ones? Don't we have mem technologies that are filling them with zeros? > Note that mtdram is artificially setting the mem-region to 0xff in its > dummy erase operation, so maybe it's a implicit rule that ->_erase() is > supposed to fill eraseblocks with 0xff. I've wondered about the general assumption. But mtdram isn't really a good example, because it clearly calls itself a "test mtd device". So it makes sense it would emulate common MTDs (i.e., flash memory). Brian
diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c index 2542f5b8b63f..02c6b9dcbd3e 100644 --- a/drivers/mtd/devices/mchp23k256.c +++ b/drivers/mtd/devices/mchp23k256.c @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi) data = dev_get_platdata(&spi->dev); + mtd_set_of_node(&flash->mtd, spi->dev.of_node); flash->mtd.dev.parent = &spi->dev; flash->mtd.type = MTD_RAM; flash->mtd.flags = MTD_CAP_RAM; @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) flash->mtd._read = mchp23k256_read; flash->mtd._write = mchp23k256_write; + flash->mtd.erasesize = PAGE_SIZE; + while (flash->mtd.size & (flash->mtd.erasesize - 1)) + flash->mtd.erasesize >>= 1; + err = mtd_device_register(&flash->mtd, data ? data->parts : NULL, data ? data->nr_parts : 0); if (err)
Setting the of_node for the mtd device allows the generic mtd code to setup the partitions. Additionally we must specify a non-zero erasesize for the partitions to be writeable. Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> --- drivers/mtd/devices/mchp23k256.c | 5 +++++ 1 file changed, 5 insertions(+)