linux-kernel - Re: [PATCH 2/3] aspeed-video: clear spurious interrupt bits unconditionally

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Message-ID: <CACPK8XczCUgqOENABoDbc-qwbMxOh=1OUyBtuHSmDG_Zo571Wg@mail.gmail.com>
Date:   Tue, 22 Dec 2020 04:47:37 +0000
From:   Joel Stanley <joel@....id.au>
To:     Zev Weiss <zev@...ilderbeest.net>
Cc:     Eddie James <eajames@...ux.ibm.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Andrew Jeffery <andrew@...id.au>, linux-media@...r.kernel.org,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
Subject: Re: [PATCH 2/3] aspeed-video: clear spurious interrupt bits unconditionally

On Tue, 15 Dec 2020 at 02:46, Zev Weiss <zev@...ilderbeest.net> wrote:
>
> Instead of testing and conditionally clearing them one by one, we can
> instead just unconditionally clear them all at once.
>
> Signed-off-by: Zev Weiss <zev@...ilderbeest.net>

I had a poke at the assembly and it looks like GCC is clearing the
bits unconditionally anyway, so removing the tests provides no change.

Combining them is a good further optimization.

Reviewed-by: Joel Stanley <joel@....id.au>

A question unrelated to this patch: Do you know why the driver doesn't
clear the status bits in the interrupt handler? I would expect it to
write the value of sts back to the register to ack the pending
interrupt.

> ---
>  drivers/media/platform/aspeed-video.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
> index eb02043532e3..218aae3be809 100644
> --- a/drivers/media/platform/aspeed-video.c
> +++ b/drivers/media/platform/aspeed-video.c
> @@ -558,6 +558,14 @@ static void aspeed_video_irq_res_change(struct aspeed_video *video, ulong delay)
>         schedule_delayed_work(&video->res_work, delay);
>  }
>
> +/*
> + * Interrupts that we don't use but have to explicitly ignore because the
> + * hardware asserts them even when they're disabled in the VE_INTERRUPT_CTRL
> + * register.
> + */
> +#define VE_SPURIOUS_IRQS \
> +       (VE_INTERRUPT_CAPTURE_COMPLETE | VE_INTERRUPT_FRAME_COMPLETE)
> +
>  static irqreturn_t aspeed_video_irq(int irq, void *arg)
>  {
>         struct aspeed_video *video = arg;
> @@ -630,15 +638,8 @@ static irqreturn_t aspeed_video_irq(int irq, void *arg)
>                         aspeed_video_start_frame(video);
>         }
>
> -       /*
> -        * CAPTURE_COMPLETE and FRAME_COMPLETE interrupts come even when these
> -        * are disabled in the VE_INTERRUPT_CTRL register so clear them to
> -        * prevent unnecessary interrupt calls.
> -        */
> -       if (sts & VE_INTERRUPT_CAPTURE_COMPLETE)
> -               sts &= ~VE_INTERRUPT_CAPTURE_COMPLETE;
> -       if (sts & VE_INTERRUPT_FRAME_COMPLETE)
> -               sts &= ~VE_INTERRUPT_FRAME_COMPLETE;
> +       /* Squash known bogus interrupts */
> +       sts &= ~VE_SPURIOUS_IRQS;
>
>         if (sts)
>                 dev_err_ratelimited(video->dev, "unexpected interrupt asserted:"
> --
> 2.29.2
>