netdev - Re: [PATCH net] Revert "net: stmmac: Specify hardware capability value when FIFO size isn't specified"

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Message-ID: <2cff81d8-9bda-4aa0-80b6-2ef92cd960a6@redhat.com>
Date: Thu, 6 Feb 2025 09:08:10 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
 Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Maxime Coquelin
 <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net] Revert "net: stmmac: Specify hardware capability
 value when FIFO size isn't specified"

On 2/5/25 1:57 PM, Russell King (Oracle) wrote:
> This reverts commit 8865d22656b4, which caused breakage for platforms
> which are not using xgmac2 or gmac4. Only these two cores have the
> capability of providing the FIFO sizes from hardware capability fields
> (which are provided in priv->dma_cap.[tr]x_fifo_size.)
> 
> All other cores can not, which results in these two fields containing
> zero. We also have platforms that do not provide a value in
> priv->plat->[tr]x_fifo_size, resulting in these also being zero.
> 
> This causes the new tests introduced by the reverted commit to fail,
> and produce e.g.:
> 
> 	stmmaceth f0804000.eth: Can't specify Rx FIFO size
> 
> An example of such a platform which fails is QEMU's npcm750-evb.
> This uses dwmac1000 which, as noted above, does not have the capability
> to provide the FIFO sizes from hardware.
> 
> Therefore, revert the commit to maintain compatibility with the way
> the driver used to work.
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Link: https://lore.kernel.org/r/4e98f967-f636-46fb-9eca-d383b9495b86@roeck-us.net
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

Given the fallout caused by the blamed commit, the imminent net PR, and
the substantial agreement about the patch already shared by many persons
on the ML, unless someone raises very serious concerns very soon, I'm
going to apply this patch (a little) earlier than the 24h grace period,
to fit the mentioned PR.

Cheers,

Paolo