linux-kernel - Re: [PATCH 1/3] PCI: dwc: Add support for vendor specific capability search

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Date:   Thu, 27 May 2021 17:19:02 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Krzysztof Wilczyński <kw@...ux.com>,
        Shradha Todi <shradha.t@...sung.com>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <jingoohan1@...il.com>, <gustavo.pimentel@...opsys.com>,
        <lorenzo.pieralisi@....com>, <robh@...nel.org>,
        <bhelgaas@...gle.com>, <pankaj.dubey@...sung.com>,
        <p.rajanbabu@...sung.com>, <hari.tv@...sung.com>,
        <niyas.ahmed@...sung.com>, <l.mehra@...sung.com>
Subject: Re: [PATCH 1/3] PCI: dwc: Add support for vendor specific capability
 search



On 5/22/2021 5:01 AM, Krzysztof Wilczyński wrote:
> External email: Use caution opening links or attachments
> 
> 
> Hi Shradha,
> 
> [...]
>> +u16 dw_pcie_find_vsec_capability(struct dw_pcie *pci, u8 vsec_cap)
>> +{
>> +     u16 vsec = 0;
>> +     u32 header;
>> +
>> +     while ((vsec = dw_pcie_find_next_ext_capability(pci, vsec,
>> +                                     PCI_EXT_CAP_ID_VNDR))) {
>> +             header = dw_pcie_readl_dbi(pci, vsec + PCI_VNDR_HEADER);
>> +             if (PCI_VNDR_HEADER_ID(header) == vsec_cap)
>> +                     return vsec;
>> +     }
>> +
>> +     return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(dw_pcie_find_vsec_capability);
> 
> A small question as I am curious: why not use pci_find_vsec_capability()
> here?  The implementation looks very similar, which is why I am asking,
> but it might be that I am missing something, and for that I apologise in
> advance.
pci_find_vsec_capability() expects struct pci_dev * which we get only 
after enumeration is done. In the current scenario, we are still in 
pre-link up phase and don't have struct pci_dev * yet, hence this 
implementation, right Shradha??

> 
>          Krzysztof
>