linux-kernel - RE: [PATCH v2 04/15] PCI: Add pci_find_vsec

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Message-ID: <DM5PR12MB1835224A170AAF195EDDF88BDAB49@DM5PR12MB1835.namprd12.prod.outlook.com>
Date:   Wed, 3 Feb 2021 09:58:54 +0000
From:   Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>
To:     Lukas Wunner <lukas@...ner.de>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: RE: [PATCH v2 04/15] PCI: Add pci_find_vsec_capability() to find a
 specific VSEC

On Wed, Feb 3, 2021 at 9:36:54, Lukas Wunner <lukas@...ner.de> wrote:

> On Wed, Feb 03, 2021 at 09:11:03AM +0000, Gustavo Pimentel wrote:
> > On Wed, Feb 3, 2021 at 7:51:3, Lukas Wunner <lukas@...ner.de> wrote:
> > > On Wed, Feb 03, 2021 at 01:54:49AM +0000, Gustavo Pimentel wrote:
> > > > On Tue, Feb 2, 2021 at 18:8:55, Lukas Wunner <lukas@...ner.de> wrote:
> > > > > As the name implies, the capability is "vendor-specific", so it is
> > > > > perfectly possible that two vendors use the same VSEC ID for different
> > > > > things.
> > > > > 
> > > > > To make sure you're looking for the right capability, you need to pass
> > > > > a u16 vendor into this function and bail out if dev->vendor is
> > > > > different.
> > > > 
> > > > This function will be called by the driver that will pass the correct 
> > > > device which will be already pointing to the config space associated with
> > > > the endpoint for instance. Because the driver is already attached to the 
> > > > endpoint through the vendor ID and device ID specified, there is no need 
> > > > to do that validation, it will be redundant.
> > > 
> > > Okay.  Please amend the kernel-doc to make it explicit that it's the
> > > caller's responsibility to check the vendor ID.
> > 
> > I don't think that would be necessary, as I said, the 'struct pci_dev *' 
> > already points exclusively for the device' config space, which contains 
> > all the capabilities for that particular device by his turn will be 
> > attached to a specific driver by the Vendor and Device IDs to a specific 
> > driver, that will know, firstly search for the specific device vendor ID, 
> >  and then secondly how to decode it, and thirdly to do something with it.
> 
> The helper you're adding may not only be called from drivers but also
> from generic PCI code (such as set_pcie_thunderbolt()).  In that case
> the vendor ID is arbitrary.  Also, it doesn't *hurt* documenting this
> requirement, does it?

I understand now your PoV. In that case, I can add that info to the 
function comment.

> 
> Thanks,
> 
> Lukas