Re: [PATCH 0/1] net: stmmac: descriptor management issue during PM sequence

[Thomas BOURGOIN <thomas.bourgoin@foss.st.com>]

> Hi Thomas,
> 
> On 10/27/26 16:05, Thomas Bourgoin wrote:
>> Hello,
>>
>> During low power sequence on STM32MP21 we sometimes observe out of range access
>> to the DDR by the GMAC ethernet. I managed to narrow down the issue to the
>> resume sequence of the RX descriptors with the function
>> stmmac_clear_descriptors().
>>
>> On resume, stmmac_clear_descriptors() returns RX descriptors to the DMA
>> without restoring their buffer addresses. On DWMAC4, the DMA will
>> therefore consider a descriptor for the application as one for the DMA.
>> This can lead to illegal access from the DMA anywhere.
>> On STM32MP21 the DMA address bus is 40 bits, thus the extended status from the
>> write-back descriptor is read as an high address by the DMA. DMA will then try
>> to write in the DDR at 0x100000000 whereas on STM32MP215f-dk DDR is only 2Gb
>> from 0x8000 0000 to 0xffff ffff and nothing is mapped at 0x100000000.
>> All the other SoCs of the STM32MP1x or STM32MP2x are using a GMAC with a 32bits
>> DMA address, so I do not have illegal attemps.
>>
>> To fix this, I propose to reconstruct the RX descriptors that have been used by
>> the DMA but not forwarded to the NAPI function stmmac_rx() before suspend.
>>
>> I'm not used to this driver especially the xsk management and zero copy part.
>> Since this driver is used by a lot of plateforms I'm open to all suggestions.
>>
>> This V1 propose to reuse stmmac_init_rx_buffers() but maybe using
>> stmmac_refill() would better fit the issue. From what I read, I could not call
>> stmmac_refill() as rx_q->cur_rx is only updated in stmmac_rx(), so
>> stmmac_rx_dirty() returns 0.
> 
> 
> 

Hi Maxime

> Thanks for the series :) However it looks like this is already being 
 > addressed by
> Ding Hui's series (currently in V5) :
>
> https://lore.kernel.org/r/20261025100636.613670-1-dinghui1111@163.com
>
> Can you take a look and maybe provide some reviews/tested-by tags ?

Thanks, for the sharing. I guess I'm not the first to have the issue :)

At first glance, the v5 seems really close to the solution I proposed 
(update init descriptor function to factorize some code so it can be 
used during resume to reconstruct the descriptors that have been used by 
the GMAC DMA).

I'll take a closer look at the series, I'll try to test on 
STM32MP215F-DK but I'm not sure of what I can do.

Do you think, this patch is a candidate for LTS ?

Regards,

Thomas