[U-Boot] nios2: nios2-generic: do not allocate rx buf in net.c

Do not allocate rx buf in net.c, because altera_tse allocates
its own rx buf in driver. This can save 6KB memory.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
---
 include/configs/nios2-generic.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

On Thursday, November 05, 2015 at 09:42:43 AM, Thomas Chou wrote:
> Do not allocate rx buf in net.c, because altera_tse allocates
> its own rx buf in driver. This can save 6KB memory.
> 
> Signed-off-by: Thomas Chou <thomas@wytron.com.tw>

Shouldn't we instead fix the altera driver to use the pre-allocated
buffer ?

Best regards,
Marek Vasut

Hi Marek,

On 2015年11月06日 00:16, Marek Vasut wrote:
> On Thursday, November 05, 2015 at 09:42:43 AM, Thomas Chou wrote:
>> Do not allocate rx buf in net.c, because altera_tse allocates
>> its own rx buf in driver. This can save 6KB memory.
>>
>> Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
>
> Shouldn't we instead fix the altera driver to use the pre-allocated
> buffer ?

It should not. The drivers and devices are dynamically binding in driver 
model. The buffers used by devices should be allocated per device. Eg, 
there may be multiple ethernet devices and they should not use the same 
pre-allocated rx bufs.

Best regards,
Thomas

On Friday, November 06, 2015 at 12:47:13 AM, Thomas Chou wrote:
> Hi Marek,

Hi!

> On 2015年11月06日 00:16, Marek Vasut wrote:
> > On Thursday, November 05, 2015 at 09:42:43 AM, Thomas Chou wrote:
> >> Do not allocate rx buf in net.c, because altera_tse allocates
> >> its own rx buf in driver. This can save 6KB memory.
> >> 
> >> Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
> > 
> > Shouldn't we instead fix the altera driver to use the pre-allocated
> > buffer ?
> 
> It should not. The drivers and devices are dynamically binding in driver
> model. The buffers used by devices should be allocated per device. Eg,
> there may be multiple ethernet devices and they should not use the same
> pre-allocated rx bufs.

Oh ok, I see your point now. But then, this allocation of buffers in the
ethernet drivers becomes a boilerplate code, right ? So maybe there should
be some mechanism in the network stack to allocate the buffers for the drivers
to prevent duplication of code.

What do you think?

Best regards,
Marek Vasut

Hi Marek,

On 2015年11月06日 09:40, Marek Vasut wrote:
> On Friday, November 06, 2015 at 12:47:13 AM, Thomas Chou wrote:
>> Hi Marek,
>
> Hi!
>
>> On 2015年11月06日 00:16, Marek Vasut wrote:
>>> On Thursday, November 05, 2015 at 09:42:43 AM, Thomas Chou wrote:
>>>> Do not allocate rx buf in net.c, because altera_tse allocates
>>>> its own rx buf in driver. This can save 6KB memory.
>>>>
>>>> Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
>>>
>>> Shouldn't we instead fix the altera driver to use the pre-allocated
>>> buffer ?
>>
>> It should not. The drivers and devices are dynamically binding in driver
>> model. The buffers used by devices should be allocated per device. Eg,
>> there may be multiple ethernet devices and they should not use the same
>> pre-allocated rx bufs.
>
> Oh ok, I see your point now. But then, this allocation of buffers in the
> ethernet drivers becomes a boilerplate code, right ? So maybe there should
> be some mechanism in the network stack to allocate the buffers for the drivers
> to prevent duplication of code.

The pre-alloacted tx_buf is still in use by net/ . But most ethernet 
drivers allocate their own rx_buf (perhaps as ring buffer). Most of them 
use memalign(PKTSIZE_ALIGN), which is the same as 
malloc_cache_aligned(PKTSIZE_ALIGN). Each driver may have different 
requirement of size/number of the rx buf.

The driver passes the rx buf to net/ . And the net/ return the rx buf 
with free_pkt() to the driver after use.

I think this scheme works fine. There not much duplication of code for 
rx_buf allocation, which might be only a malloc_cache_aligned().

Best regards,
Thomas