linux-kernel - Re: [PATCH v7 5/5] PCI/AER: Only clear error bits in pcie_clear_device

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Message-ID: <881e57b7-aa73-4df6-b37b-d71571567436@linux.alibaba.com>
Date: Wed, 28 Jan 2026 20:45:36 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, bhelgaas@...gle.com, kbusch@...nel.org,
 sathyanarayanan.kuppuswamy@...ux.intel.com, mahesh@...ux.ibm.com,
 oohall@...il.com, terry.bowman@....com, tianruidong@...ux.alibaba.com,
 lukas@...ner.de
Subject: Re: [PATCH v7 5/5] PCI/AER: Only clear error bits in
 pcie_clear_device_status()



On 1/27/26 6:45 PM, Jonathan Cameron wrote:
> On Sat, 24 Jan 2026 15:45:57 +0800
> Shuai Xue <xueshuai@...ux.alibaba.com> wrote:
> 
>> Currently, pcie_clear_device_status() clears the entire PCIe Device
>> Status register (PCI_EXP_DEVSTA), which includes both error status bits
>> and other status bits such as AUX Power Detected (AUXPD) and
>> Transactions Pending (TRPND).
>>
>> Clearing non-error status bits can interfere with other drivers or
>> subsystems that may rely on these bits. To fix it, only clear the error
>> bits (0xf) while preserving other status bits.
>>
>> Fixes: ec752f5d54d7 ("PCI/AER: Clear device status bits during ERR_FATAL and ERR_NONFATAL")
>> Cc: stable@...r.kernel.org
>> Suggested-by: Lukas Wunner <lukas@...ner.de>
>> Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
> Similar to previous. Drag to start of series to make backports easier if
> we think this is a fix that affects real cases.  

Thank you for the detailed feedback.

I'll move this patch to the start of the series for easier backporting.

> For stuff that's defined
> in the PCI 6.2 spec, AUX power and Transactions Pending are RO, but
> the interesting one is Emergency Power Reduction Detected which is RW1C
> and hence reason this fix is potentially needed  + future features using
> remaining bits.
> 
> I'd be more explicit in the commit message for that.  Talk about it not
> mattering for AUXPD or TRPND because they are RO, vs the ones we
> aren't using yet in Linux with the emergency power reduction detected
> as an example that clearly shows we need to mask this!
> 

You're absolutely right - the commit
message should be more explicit about the different bit types and their
implications.

The revised the commit message is:

PCI/AER: Only clear error bits in PCIe Device Status register

Currently, pcie_clear_device_status() clears the entire PCIe Device
Status register (PCI_EXP_DEVSTA), which includes both error status bits
and other status bits.

According to PCIe Base Spec r6.0 sec 7.5.3.5, the Device Status register
contains different types of status bits:

- Read-only bits (AUXPD, TRPND): Writing to these has no effect, but
   clearing them is unnecessary.

- RW1C (read/write 1 to clear) non-error bits: For example, Emergency
   Power Reduction Detected (bit 6). Unconditionally clearing these bits
   can interfere with other drivers or subsystems that rely on them.

- Reserved bits: May be used for future features and should be preserved.

To prevent unintended side effects, modify pcie_clear_device_status() to
only clear the four error status bits (CED, NFED, FED, URD) while
preserving all other status bits.

Fixes: ec752f5d54d7 ("PCI/AER: Clear device status bits during ERR_FATAL and ERR_NONFATAL")
Cc: stable@...r.kernel.org
Suggested-by: Lukas Wunner <lukas@...ner.de>
Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>

> J

Thanks.

Best Regards,
Shuai