linux-kernel - Re: [v2] PCI: cadence: Add configuration space capability search API

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Message-ID: <0abc7fc9-3370-4f54-a230-ecc044928fcc@163.com>
Date: Fri, 21 Mar 2025 09:09:35 +0800
From: Hans Zhang <18255117159@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Siddharth Vadapalli <s-vadapalli@...com>, lpieralisi@...nel.org,
 kw@...ux.com, robh@...nel.org, bhelgaas@...gle.com, bwawrzyn@...co.com,
 thomas.richard@...tlin.com, wojciech.jasko-EXT@...tinental-corporation.com,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [v2] PCI: cadence: Add configuration space capability search API



On 2025/3/21 05:28, Bjorn Helgaas wrote:
> On Sat, Mar 15, 2025 at 08:06:52AM +0800, Hans Zhang wrote:
>> On 2025/3/15 04:31, Bjorn Helgaas wrote:
>>> On Fri, Mar 14, 2025 at 06:35:11PM +0530, Manivannan Sadhasivam wrote:
>>>> ...
>>>
>>>> Even though this patch is mostly for an out of tree controller
>>>> driver which is not going to be upstreamed, the patch itself is
>>>> serving some purpose. I really like to avoid the hardcoded offsets
>>>> wherever possible. So I'm in favor of this patch.
>>>>
>>>> However, these newly introduced functions are a duplicated version
>>>> of DWC functions. So we will end up with duplicated functions in
>>>> multiple places. I'd like them to be moved (both this and DWC) to
>>>> drivers/pci/pci.c if possible. The generic function
>>>> *_find_capability() can accept the controller specific readl/ readw
>>>> APIs and the controller specific private data.
>>>
>>> I agree, it would be really nice to share this code.
>>>
>>> It looks a little messy to deal with passing around pointers to
>>> controller read ops, and we'll still end up with a lot of duplicated
>>> code between __pci_find_next_cap() and __cdns_pcie_find_next_cap(),
>>> etc.
>>>
>>> Maybe someday we'll make a generic way to access non-PCI "config"
>>> space like this host controller space and PCIe RCRBs.
>>>
>>> Or if you add interfaces that accept read/write ops, maybe the
>>> existing pci_find_capability() etc could be refactored on top of them
>>> by passing in pci_bus_read_config_word() as the accessor.
>>
>> I have already replied to an email, please help review whether it is
>> appropriate.
> 
> URL to the email on lore.kernel.org?
> 
> If you mean this:
> https://lore.kernel.org/r/3cadf8d5-c4d8-4941-ae2e-8b00ceb83a8f@163.com,
> just post it as a v3 patch with the usual commit log and motivation
> for the change, and it will automatically get picked up in patchwork
> so it doesn't get forgotten.
> 
> Right now the urgency seems fairly low since (IIUC) it doesn't fix an
> existing bug in the upstream code.

Hi Bjorn,

Thanks your for reply. I will submit v3 patch.

Best regards,
Hans