linux-kernel - Re: [PATCH v3] PCI/DOE: Expose the DOE protocols via sysfs

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Date:   Thu, 10 Aug 2023 07:05:12 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Alistair Francis <alistair23@...il.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        Jonathan.Cameron@...wei.com, lukas@...ner.de,
        alex.williamson@...hat.com, christian.koenig@....com,
        kch@...dia.com, logang@...tatee.com, linux-kernel@...r.kernel.org,
        Alistair Francis <alistair.francis@....com>
Subject: Re: [PATCH v3] PCI/DOE: Expose the DOE protocols via sysfs

On Wed, Aug 09, 2023 at 07:28:51PM -0400, Alistair Francis wrote:
> The PCIe 6 specification added support for the Data Object Exchange (DOE).
> When DOE is supported the Discovery Data Object Protocol must be
> implemented. The protocol allows a requester to obtain information about
> the other DOE protocols supported by the device.
> 
> The kernel is already querying the DOE protocols supported and cacheing
> the values. This patch exposes the values via sysfs. This will allow
> userspace to determine which DOE protocols are supported by the PCIe
> device.
> 
> By exposing the information to userspace tools like lspci can relay the
> information to users. By listing all of the supported protocols we can
> allow userspace to parse and support the list, which might include
> vendor specific protocols as well as yet to be supported protocols.
> 
> Signed-off-by: Alistair Francis <alistair.francis@....com>
> ---
> v3:
>  - Expose each DOE feature as a separate file

But you don't actually have anything in the sysfs files, why not?

> --- a/drivers/pci/doe.c
> +++ b/drivers/pci/doe.c
> @@ -56,6 +56,10 @@ struct pci_doe_mb {
>  	wait_queue_head_t wq;
>  	struct workqueue_struct *work_queue;
>  	unsigned long flags;
> +
> +#ifdef CONFIG_SYSFS
> +	struct device_attribute *sysfs_attrs;
> +#endif

Please don't put #ifdefs in .c files if you can prevent it.  I think
this will work just fine if you don't have the #ifdef.  And who would be
using pci without sysfs?

> +		attrs[i].attr.mode = 0444;
> +		attrs[i].show = NULL;

Why set to NULL something that is already NULL?  Did you just forget to
actually set the proper show callback here?

> +#ifdef CONFIG_PCI_DOE
> +	retval = doe_sysfs_init(pdev);
> +	if (retval)
> +		return retval;
> +#endif

Again, no #ifdef in .c files please, put this in the .h file like
normal.

thanks,

greg k-h