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SubjectRe: [PATCH] mmc: dw_mmc: Don't allow Runtime PM for SDIO cards
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On 04/12/2017 07:55 AM, Douglas Anderson wrote:
> According to the SDIO standard interrupts are normally signalled in a
> very complicated way. They require the card clock to be running and
> require the controller to be paying close attention to the signals
> coming from the card. This simply can't happen with the clock stopped
> or with the controller in a low power mode.
>
> To that end, we'll disable runtime_pm when we detect that an SDIO card
> was inserted. This is much like with what we do with the special
> "SDMMC_CLKEN_LOW_PWR" bit that dw_mmc supports.
>
> NOTE: we specifically do this Runtime PM disabling at card init time
> rather than in the enable_sdio_irq() callback. This is _different_
> than how SDHCI does it. Why do we do it differently?
>
> - Unlike SDHCI, dw_mmc uses the standard sdio_irq code in Linux (AKA
> dw_mmc doesn't set MMC_CAP2_SDIO_IRQ_NOTHREAD).
> - Because we use the standard sdio_irq code:
> - We see a constant stream of enable_sdio_irq(0) and
> enable_sdio_irq(1) calls. This is because the standard code
> disables interrupts while processing and re-enables them after.
> - While interrupts are disabled, there's technically a period where
> we could get runtime disabled while processing interrupts.
> - If we are runtime disabled while processing interrupts, we'll
> reset the controller at resume time (see dw_mci_runtime_resume),
> which seems like a terrible idea because we could possibly have
> another interrupt pending.
>
> To fix the above isues we'd want to put something in the standard
> sdio_irq code that makes sure to call pm_runtime get/put when
> interrupts are being actively being processed. That's possible to do,
> but it seems like a more complicated mechanism when we really just
> want the runtime pm disabled always for SDIO cards given that all the
> other bits needed to get Runtime PM vs. SDIO just aren't there.
>
> NOTE: at some point in time someone might come up with a fancy way to
> do SDIO interrupts and still allow (some) amount of runtime PM.
> Technically we could turn off the card clock if we used an alternate
> way of signaling SDIO interrupts (and out of band interrupt is one way
> to do this). We probably wouldn't actually want to fully runtime
> suspend in this case though--at least not with the current
> dw_mci_runtime_resume() which basically fully resets the controller at
> resume time.
>
> Fixes: e9ed8835e990 ("mmc: dw_mmc: add runtime PM callback")
> Cc: <stable@vger.kernel.org>
> Reported-by: Brian Norris <briannorris@chromium.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Acked-by: Jaehoon Chung <jh80.chung@samsung.com>

Best Regards,
Jaehoon Chung

> ---
> drivers/mmc/host/dw_mmc.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 249ded65192e..e45129f48174 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -23,6 +23,7 @@
> #include <linux/ioport.h>
> #include <linux/module.h>
> #include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> #include <linux/seq_file.h>
> #include <linux/slab.h>
> #include <linux/stat.h>
> @@ -1620,10 +1621,16 @@ static void dw_mci_init_card(struct mmc_host *mmc, struct mmc_card *card)
>
> if (card->type == MMC_TYPE_SDIO ||
> card->type == MMC_TYPE_SD_COMBO) {
> - set_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags);
> + if (!test_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags)) {
> + pm_runtime_get_noresume(mmc->parent);
> + set_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags);
> + }
> clk_en_a = clk_en_a_old & ~clken_low_pwr;
> } else {
> - clear_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags);
> + if (test_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags)) {
> + pm_runtime_put_noidle(mmc->parent);
> + clear_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags);
> + }
> clk_en_a = clk_en_a_old | clken_low_pwr;
> }
>
>

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