netdev - Re: [PATCH] net: bcmgenet: Reset RBUF on first open

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Message-ID: <47ba4ef5a42fe7412d7e3432a0995464@rmail.be>
Date: Mon, 26 Feb 2024 20:14:54 +0100
From: Maarten <maarten@...il.be>
To: Florian Fainelli <florian.fainelli@...adcom.com>
Cc: Doug Berger <opendmb@...il.com>, netdev@...r.kernel.org, Broadcom
 internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, Phil
 Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH] net: bcmgenet: Reset RBUF on first open

Florian Fainelli schreef op 2024-02-26 18:34:
> On 2/23/24 15:53, Maarten Vanraes wrote:
>> From: Phil Elwell <phil@...pberrypi.com>
>> 
>> If the RBUF logic is not reset when the kernel starts then there
>> may be some data left over from any network boot loader. If the
>> 64-byte packet headers are enabled then this can be fatal.
>> 
>> Extend bcmgenet_dma_disable to do perform the reset, but not when
>> called from bcmgenet_resume in order to preserve a wake packet.
>> 
>> N.B. This different handling of resume is just based on a hunch -
>> why else wouldn't one reset the RBUF as well as the TBUF? If this
>> isn't the case then it's easy to change the patch to make the RBUF
>> reset unconditional.
> 
> The real question is why is not the boot loader putting the GENET core
> into a quasi power-on-reset state, since this is what Linux expects,
> and also it seems the most conservative and prudent approach. Assuming
> the RDMA and Unimac RX are disabled, otherwise we would happily
> continuing to accept packets in DRAM, then the question is why is not
> the RBUF flushed too, or is it flushed, but this is insufficient, if
> so, have we determined why?

I can only say that when I was testing upstream kernels (6.7, 6.8) I had 
a lot of issue rebooting the RPI4B, and after some searched, I found 
this patch in the raspberrypi kernel (from 2020) and since I've used it, 
I do not have this issue anymore for at least 10 boots. Not sure if I 
should've added a Tested-By with myself?

>> 
>> See: https://github.com/raspberrypi/linux/issues/3850
>> 
>> Signed-off-by: Phil Elwell <phil@...pberrypi.com>
>> Signed-off-by: Maarten Vanraes <maarten@...il.be>
>> ---
>>   drivers/net/ethernet/broadcom/genet/bcmgenet.c | 16 ++++++++++++----
>>   1 file changed, 12 insertions(+), 4 deletions(-)
>> 
>> This patch fixes a problem on RPI 4B where in ~2/3 cases (if you're 
>> using
>> nfsroot), you fail to boot; or at least the boot takes longer than
>> 30 minutes.
> 
> This makes me wonder whether this also fixes the issues that Maxime
> reported a long time ago, which I can reproduce too, but have not been
> able to track down the source of:
> 
> https://lore.kernel.org/linux-kernel/20210706081651.diwks5meyaighx3e@gilmour/
> 
>> 
>> Doing a simple ping revealed that when the ping starts working again
>> (during the boot process), you have ping timings of ~1000ms, 2000ms or
>> even 3000ms; while in normal cases it would be around 0.2ms.
> 
> I would prefer that we find a way to better qualify whether a RBUF
> reset is needed or not, but I suppose there is not any other way,
> since there is an "RBUF enabled" bit that we can key off.
> 
> Doug, what do you think?