Re: [PATCH net v4 5/7] net: stmmac: dwmac4: Use the correct bufzise when the len is exactly 8K

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

On 9/18/26 14:25, Nicolai Buchwitz wrote:
> Hi Maxime
> 
> On 17.9.2026 23:53, Maxime Chevallier wrote:
>> DMA bufsize selection isn't made on the MTU but the actual frame length,
>> so including the L2 header. On DWMAC4, if the len is exactly BUF_SIZE_8KiB,
>> the next larger size is incorrectly selected.
>>
>> Lets fix the comparison and while at it, rename the parameter from len
>> to mtu.
> 
> Isn't it "[...] from mtu to len"?

:(

Bah, if respin is required I'll fix this

>>
>> Fixes: c3efed5ad1b0 ("net: stmmac: Enable dwmac4 jumbo frame more than 8KiB").
>> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
>> ---
>>  drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c | 4 ++--
>>  drivers/net/ethernet/stmicro/stmmac/hwif.h         | 2 +-
>>  drivers/net/ethernet/stmicro/stmmac/ring_mode.c    | 4 ++--
>>  3 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
>> index 2994df41ec2c..c6a8f8d73501 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
>> @@ -474,11 +474,11 @@ static void dwmac4_set_sarc(struct dma_desc *p, u32 sarc_type)
>>                        sarc_type));
>>  }
>>
>> -static int set_16kib_bfsize(int mtu)
>> +static int set_16kib_bfsize(int len)
>>  {
>>      int ret = 0;
>>
>> -    if (unlikely(mtu >= BUF_SIZE_8KiB))
>> +    if (unlikely(len > BUF_SIZE_8KiB))
> 
> Should we drop set_16kib_bfsize() instead?
> 
> After 6/7 it looks to me like the same test as the first branch of
> stmmac_set_bfsize(). The caller ends up there anyway when it returns 0
> and chain_mode_ops doesn't have it at all.

True yeah :) however maybe we can wait for this to be merged and have the
cleanup in net-next ?

Sashiko is getting crazy with the "pre-existing issues" everytime we touch
stmmac, cleanups are long overdue and this could be included in there :(

Maxime