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

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Date:   Wed, 23 Dec 2020 01:07:12 +0000
From:   Joel Stanley <joel@....id.au>
To:     Zev Weiss <zev@...ilderbeest.net>,
        Ryan Chen <ryan_chen@...eedtech.com>
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, 22 Dec 2020 at 19:14, Zev Weiss <zev@...ilderbeest.net> wrote:
>
> On Mon, Dec 21, 2020 at 10:47:37PM CST, Joel Stanley wrote:
> >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.
> >
>
> No, I don't, and I was sort of wondering the same thing actually -- I'm
> not deeply familiar with this hardware or driver though, so I was a bit
> hesitant to start messing with things.  (Though maybe doing so would
> address the "stickiness" aspect when it does manifest.)  Perhaps Eddie
> or Jae can shed some light here?

I think you're onto something here - this would be why the status bits
seem to stick until the device is reset.

Until Aspeed can clarify if this is a hardware or software issue, I
suggest we ack the bits and log a message when we see them, instead of
always ignoring them without taking any action.

Can you write a patch that changes the interrupt handler to ack status
bits as it handles each of them?

>
>
> Zev
>