linux-kernel - Re: [PATCH 1/1] PCI: Fix Extend ACS configurability

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Message-ID: <4d5224c6-bc0b-4ca9-9f1a-71d701554b3d@nvidia.com>
Date: Thu, 16 Jan 2025 17:21:29 -0800
From: Tushar Dave <tdave@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: corbet@....net, bhelgaas@...gle.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, vidyas@...dia.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, vsethi@...dia.com,
 sdonthineni@...dia.com
Subject: Re: [PATCH 1/1] PCI: Fix Extend ACS configurability



On 1/16/25 11:01, Jason Gunthorpe wrote:
> On Wed, Jan 15, 2025 at 07:11:25PM -0800, Tushar Dave wrote:
>> @@ -1028,10 +1032,15 @@ static void __pci_config_acs(struct pci_dev *dev,
>> struct pci_acs *caps,
>>
>>          pci_dbg(dev, "ACS mask  = %#06x\n", mask);
>>          pci_dbg(dev, "ACS flags = %#06x\n", flags);
>> +       pci_dbg(dev, "ACS control = %#06x\n", caps->ctrl);
>> +       pci_dbg(dev, "ACS fw_ctrl = %#06x\n", caps->fw_ctrl);
>>
>>          /* If mask is 0 then we copy the bit from the firmware setting. */
>> -       caps->ctrl = (caps->ctrl & ~mask) | (caps->fw_ctrl & mask);
>> -       caps->ctrl |= flags;
>> +       caps->ctrl = (caps->ctrl & mask) | (caps->fw_ctrl & ~mask);
>> +
>> +       /* Apply the flags */
>> +       caps->ctrl &= ~mask;
>> +       caps->ctrl |= (flags & mask);
> 
> caps->ctrl = (caps->ctrl & mask) & ~mask == 0 - so this is kind of confusing.
> 
> What we want is to take the fw_ctl for all bits where mask is 0 and
> take flags for all bits where it is 1?
> 
>    caps->ctrl = (caps->fw_ctrl & ~mask) | (flags & mask);
> 
> ?

Yes :)

-       /* If mask is 0 then we copy the bit from the firmware setting. */
-       caps->ctrl = (caps->ctrl & ~mask) | (caps->fw_ctrl & mask);
-       caps->ctrl |= flags;
+       /* For mask bits that are 0 copy them from the firmware setting
+        * and apply flags for all the mask bits that are 1.
+        */
+       caps->ctrl = (caps->fw_ctrl & ~mask) | (flags & mask);


I ran some sanity tests and looks good. Can I send V2 now?

-Tushar

> 
> Jason