Re: [PATCH] PCI: Change message to debug level in pci_set_cacheline_size

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Dec 08, 2020 at 06:57:02PM +0100, Heiner Kallweit wrote:
> Drivers like ehci_hcd and xhci_hcd use pci_set_mwi() and emit an
> annnoying message like the following that results in user questions
> whether something is broken.
> xhci_hcd 0000:00:15.0: cache line size of 64 is not supported
> 
> Root cause of the message is that on several (most?) chips the
> cache line size register is hard-wired to 0.

Interesting.  Per spec, for PCIe, I think the Cache Line Size is
supposed to be read/write except on virtual functions, where it is RO
Zero (and the example above doesn't look like a VF).  It doesn't *do*
anything for most PCIe devices, but it's still supposed to be
writable.

But it's not completely clear for conventional PCI -- PCI r3.0, sec
6.2.4, says the register "must be implemented by master devices that
can generate the Memory Write and Invalidate command."  So I guess if
a device doesn't support MWI, maybe it doesn't have to be writable.

Applied to pci/misc for v5.11, thanks!

> Change this message to debug level, an interested caller can still
> inform the user (if deemed helpful) based on the return code.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>  drivers/pci/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b7f0883d6..9a5500287 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4324,7 +4324,7 @@ int pci_set_cacheline_size(struct pci_dev *dev)
>  	if (cacheline_size == pci_cache_line_size)
>  		return 0;
>  
> -	pci_info(dev, "cache line size of %d is not supported\n",
> +	pci_dbg(dev, "cache line size of %d is not supported\n",
>  		   pci_cache_line_size << 2);
>  
>  	return -EINVAL;
> -- 
> 2.29.2
>