netdev - Re: [PATCH 1/2] PCI/MSI: Add MSIX option to write to ENTRY

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Message-ID: <4f621a9d-f527-4148-831b-aad577a6e097@redhat.com>
Date: Thu, 21 Nov 2024 11:28:28 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Dullfire <dullfire@...oo.com>, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Jacob Keller
 <jacob.e.keller@...el.com>, Simon Horman <horms@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Mostafa Saleh <smostafa@...gle.com>,
 Marc Zyngier <maz@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: Re: [PATCH 1/2] PCI/MSI: Add MSIX option to write to ENTRY_DATA
 before any reads

On 11/21/24 10:22, Dullfire wrote:
> On 11/21/24 02:55, Paolo Abeni wrote:
>> On 11/18/24 00:48, dullfire@...oo.com wrote:
>>> From: Jonathan Currier <dullfire@...oo.com>
>>>
>>> Commit 7d5ec3d36123 ("PCI/MSI: Mask all unused MSI-X entries")
>>> introduces a readl() from ENTRY_VECTOR_CTRL before the writel() to
>>> ENTRY_DATA. This is correct, however some hardware, like the Sun Neptune
>>> chips, the niu module, will cause an error and/or fatal trap if any MSIX
>>> table entry is read before the corresponding ENTRY_DATA field is written
>>> to. This patch adds an optional early writel() in msix_prepare_msi_desc().
>> Why the issue can't be addressed into the relevant device driver? It
>> looks like an H/W bug, a driver specific fix looks IMHO more fitting.
>
> I considered this approach, and thus asked about it in the mailing lists here:
> https://lore.kernel.org/sparclinux/7de14cca-e2fa-49f7-b83e-5f8322cc9e56@yahoo.com/T/

I forgot about such thread, thank you for the reminder. Since the more
hackish code is IRQ specific, if Thomas is fine with that, I'll not oppose.

>> A cross subsystem series, like this one, gives some extra complication
>> to maintainers.

The niu driver is not exactly under very active development, I guess the
whole series could go via the IRQ subsystem, if Thomas agrees.

Cheers,

Paolo