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SubjectRe: [PATCH 05/11] mmc: core: Clarify sdio_irq_pending flag for MMC_CAP2_SDIO_IRQ_NOTHREAD
Hi,

On Tue, Sep 3, 2019 at 7:22 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> In the single SDIO IRQ handler case, the sdio_irq_pending flag is used to
> avoid reading the SDIO_CCCR_INTx register and instead immediately call the
> SDIO func's >irq_handler() callback.
>
> To clarify the use behind the flag for the MMC_CAP2_SDIO_IRQ_NOTHREAD case,
> let's set the flag from inside sdio_signal_irq(), rather from
> sdio_run_irqs().

I'm having a hard time parsing the above statement... Can you reword
and maybe I'll understand?


> Moreover, let's also reset the flag when the SDIO IRQ have
> been properly processed.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
> drivers/mmc/core/sdio_irq.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)

Nice! This looks like it addresses some of the things that came up in
the previous discussion [1] and should be a nice improvement. From
re-reading that discussion that will probably change the behvaior
slightly (hopefully for the better) in the single-function case where
we might actually poll CCCR_INTx sometimes now.


> diff --git a/drivers/mmc/core/sdio_irq.c b/drivers/mmc/core/sdio_irq.c
> index f75043266984..0962a4357d54 100644
> --- a/drivers/mmc/core/sdio_irq.c
> +++ b/drivers/mmc/core/sdio_irq.c
> @@ -59,6 +59,7 @@ static int process_sdio_pending_irqs(struct mmc_host *host)
> {
> struct mmc_card *card = host->card;
> int i, ret, count;
> + bool sdio_irq_pending = host->sdio_irq_pending;
> unsigned char pending;
> struct sdio_func *func;
>
> @@ -66,13 +67,16 @@ static int process_sdio_pending_irqs(struct mmc_host *host)
> if (mmc_card_suspended(card))
> return 0;
>
> + /* Clear the flag to indicate that we have processed the IRQ. */
> + host->sdio_irq_pending = false;
> +
> /*
> * Optimization, if there is only 1 function interrupt registered
> * and we know an IRQ was signaled then call irq handler directly.
> * Otherwise do the full probe.
> */
> func = card->sdio_single_irq;
> - if (func && host->sdio_irq_pending) {
> + if (func && sdio_irq_pending) {
> func->irq_handler(func);
> return 1;
> }
> @@ -110,7 +114,6 @@ static void sdio_run_irqs(struct mmc_host *host)
> {
> mmc_claim_host(host);
> if (host->sdio_irqs) {
> - host->sdio_irq_pending = true;
> process_sdio_pending_irqs(host);
> if (host->ops->ack_sdio_irq)
> host->ops->ack_sdio_irq(host);
> @@ -128,6 +131,7 @@ void sdio_irq_work(struct work_struct *work)
>
> void sdio_signal_irq(struct mmc_host *host)
> {
> + host->sdio_irq_pending = true;

Is this safe to do without claiming the host or any other type of
locking? sdio_signal_irq() is called directly from the interrupt
handler on dw_mmc with no locks held at all. Could we have races /
problems with weakly ordered memory?

Maybe I'm not understanding why this has to move. It seems like it
would have been fine to leave this part in sdio_run_irqs() where it
was...


[1] https://lore.kernel.org/r/CAD=FV=XBVRsdiOD0vhgTvMXmqm=fzy9Bzd_x=E1TNPBsT_D-tQ@mail.gmail.com

-Doug

> queue_delayed_work(system_wq, &host->sdio_irq_work, 0);
> }
> EXPORT_SYMBOL_GPL(sdio_signal_irq);
> @@ -173,7 +177,6 @@ static int sdio_irq_thread(void *_host)
> if (ret)
> break;
> ret = process_sdio_pending_irqs(host);
> - host->sdio_irq_pending = false;
> mmc_release_host(host);
>
> /*
> --
> 2.17.1
>

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