From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753239AbdDMJcz (ORCPT ); Thu, 13 Apr 2017 05:32:55 -0400 Received: from mail-vk0-f46.google.com ([209.85.213.46]:34748 "EHLO mail-vk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750952AbdDMJcu (ORCPT ); Thu, 13 Apr 2017 05:32:50 -0400 MIME-Version: 1.0 In-Reply-To: <20170411225543.987-1-dianders@chromium.org> References: <20170411225543.987-1-dianders@chromium.org> From: Ulf Hansson Date: Thu, 13 Apr 2017 11:32:48 +0200 Message-ID: Subject: Re: [PATCH] mmc: dw_mmc: Don't allow Runtime PM for SDIO cards To: Douglas Anderson Cc: Jaehoon Chung , Brian Norris , "open list:ARM/Rockchip SoC..." , Shawn Lin , Heiko Stuebner , kevin@archlinuxarm.org, Alexandru Stan , Ziyuan Xu , "# 4.0+" , "linux-mmc@vger.kernel.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12 April 2017 at 00:55, 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. Right - unless we have a possibility to re-route the SDIO irq line to GPIO irq for wake-up when the controller enters low power state. > > 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. I wonder whether this is related to SDIO IRQs but not generic to SDIO. For example, when we have a WIFI chip with a dedicated and separate IRQ line, enabling SDMMC_CLKEN_LOW_PWR could make sense. > > 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. Thanks for the detailed clarification. > > 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. I understand this "quick" fix in dw_mmc takes care of the problem. However, allow me to try to make this a bit more generic. I intend to post something within a few days. If I fail, let's go with this solution. Kind regards Uffe > > Fixes: e9ed8835e990 ("mmc: dw_mmc: add runtime PM callback") > Cc: > Reported-by: Brian Norris > Signed-off-by: Douglas Anderson > --- > 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 > #include > #include > +#include > #include > #include > #include > @@ -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; > } > > -- > 2.12.2.715.g7642488e1d-goog >