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

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Message-ID: <88a44822-9b1a-4d59-a4ce-926d12f73147@163.com>
Date: Sat, 15 Mar 2025 08:06:52 +0800
From: Hans Zhang <18255117159@....com>
To: Bjorn Helgaas <helgaas@...nel.org>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: 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 2025/3/15 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.
> 

Hi Bjorn,

I have already replied to an email, please help review whether it is 
appropriate.

Best regards,
Hans