linux-kernel - Re: [PATCH v2 2/2] switchtec: Fix unintended mask of MRPC event

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Date:   Thu, 18 Apr 2019 08:49:02 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Wesley Sheng <wesley.sheng@...rochip.com>
Cc:     kurt.schwemmer@...rosemi.com, logang@...tatee.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        wesleyshenggit@...a.com
Subject: Re: [PATCH v2 2/2] switchtec: Fix unintended mask of MRPC event

On Mon, Apr 15, 2019 at 10:41:42PM +0800, Wesley Sheng wrote:
> When running application tool switchtec-user's `firmware update` and
> `event wait` commands concurrently, sometimes the firmware update
> speed reduced evidently.
> 
> It is because when the MRPC event happened right after MRPC event
> occurrence check but before event mask loop reach to its header
> register in event ISR, the MRPC event would be masked unintentionally.
> Since there's no chance to enable it again except for a module reload,
> all the following MRPC execution completion check will be deferred to
> timeout.
> 
> Fix this bug by skipping the mask operation for MRPC event in event
> ISR, same as what we already do for LINK event.
> 
> Fixes: 52eabba5bcdb ("switchtec: Add IOCTLs to the Switchtec driver")
> Signed-off-by: Wesley Sheng <wesley.sheng@...rochip.com>
> ---
>  drivers/pci/switch/switchtec.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
> index 7df9a69..30f6e08 100644
> --- a/drivers/pci/switch/switchtec.c
> +++ b/drivers/pci/switch/switchtec.c
> @@ -1177,7 +1177,8 @@ static int mask_event(struct switchtec_dev *stdev, int eid, int idx)
>  	if (!(hdr & SWITCHTEC_EVENT_OCCURRED && hdr & SWITCHTEC_EVENT_EN_IRQ))
>  		return 0;
>  
> -	if (eid == SWITCHTEC_IOCTL_EVENT_LINK_STATE)
> +	if (eid == SWITCHTEC_IOCTL_EVENT_LINK_STATE ||
> +	    eid == SWITCHTEC_IOCTL_EVENT_MRPC_COMP)
>  		return 0;

I'm OK with this, but I do wonder why this check is in mask_event()
instead of in switchtec_event_isr().  AFAICT it doesn't depend on
anything in the mask_all_events() -> mask_event() path, and doing it
in switchtec_event_isr() would avoid the CSR read in mask_event().

But maybe it logically belongs here.  I'll merge it as-is for now.

>  	dev_dbg(&stdev->dev, "%s: %d %d %x\n", __func__, eid, idx, hdr);
> -- 
> 2.7.4
>