linux-kernel - Re: [PATCH 2/2] mmc: core: Run handlers for pending SDIO interrupts on resume

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Date:   Thu, 29 Aug 2019 10:39:47 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH 2/2] mmc: core: Run handlers for pending SDIO interrupts
 on resume

Hi,

On Thu, Aug 29, 2019 at 10:16 AM Matthias Kaehlcke <mka@...omium.org> wrote:
>
> > In one way, this change makes sense as it adopts the legacy behavior,
> > signaling "cached" SDIO IRQs also for the new SDIO irq work interface.
> >
> > However, there is at least one major concern I see with this approach.
> > That is, in the execution path for sdio_signal_irq() (or calling
> > wake_up_process() for the legacy path), we may end up invoking the
> > SDIO func's ->irq_handler() callback, as to let the SDIO func driver
> > to consume the SDIO IRQ.
> >
> > The problem with this is, that the corresponding SDIO func driver may
> > not have been system resumed, when the ->irq_handler() callback is
> > invoked.
>
> While debugging the the problem with btmrvl I found that this is
> already the case without the patch, just not during resume, but when
> suspending. The func driver suspends before the SDIO bus and
> interrupts can keep coming in. These are processed while the func
> driver is suspended, until the SDIO core starts dropping the
> interrupts.
>
> And I think it is also already true at resume time: mmc_sdio_resume()
> re-enables SDIO IRQs and disables dropping them.

I would also note that this matches the design of the normal system
suspend/resume functions.  Interrupts continue to be enabled even
after the "suspend" call is made for a device.  Presumably this is so
that the suspend function can make use of interrupts even if there is
no other reason.  If it's important for a device to stop getting
interrupts after the "suspend" function is called then it's up to that
device to re-configure the device to stop giving interrupts.

-Doug