linux-kernel - Re: [PATCH] fpga: dfl: afu: update initialization of port

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Date: Tue, 23 Jan 2024 10:20:29 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
Cc: hao.wu@...el.com, trix@...hat.com, mdf@...nel.org, yilun.xu@...el.com,
	linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fpga: dfl: afu: update initialization of port_hdr driver

On Mon, Jan 22, 2024 at 09:24:33AM -0800, Matthew Gerlach wrote:
> Revision 2 of the Device Feature List (DFL) Port feature has
> slightly different requirements than revision 1. Revision 2
> does not need the port to reset at driver startup. In fact,

Please help illustrate what's the difference between Revision 1 & 2, and
why revision 2 needs not.

> performing a port reset during driver initialization can cause
> driver race conditions when the port is connected to a different

Please reorganize this part, in this description there seems be a
software racing bug and the patch is a workaround. But the fact is port
reset shouldn't been done for a new HW.

BTW: Is there a way to tell whether the port is connected to a different
PF? Any guarantee that revision 3, 4 ... would need a port reset or not?

Thanks,
Yilun

> PCIe Physical Function (PF) than the management PF performing
> the actual port reset.
> 
> Signed-off-by: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> ---
>  drivers/fpga/dfl-afu-main.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/fpga/dfl-afu-main.c b/drivers/fpga/dfl-afu-main.c
> index c0a75ca360d6..7d7f80cd264f 100644
> --- a/drivers/fpga/dfl-afu-main.c
> +++ b/drivers/fpga/dfl-afu-main.c
> @@ -417,7 +417,18 @@ static const struct attribute_group port_hdr_group = {
>  static int port_hdr_init(struct platform_device *pdev,
>  			 struct dfl_feature *feature)
>  {
> -	port_reset(pdev);
> +	void __iomem *base;
> +	u8 rev;
> +
> +	base = dfl_get_feature_ioaddr_by_id(&pdev->dev, PORT_FEATURE_ID_HEADER);
> +
> +	rev = dfl_feature_revision(base);
> +
> +	if (rev < 2)
> +		port_reset(pdev);
> +
> +	if (rev > 2)
> +		dev_info(&pdev->dev, "unexpected port feature revision, %u\n", rev);

Remove the print. It is indicating an error but the function returns OK.

Thanks,
Yilun

>  
>  	return 0;
>  }
> -- 
> 2.34.1
> 
>