linux-kernel - RE: [PATCH 1/2] mmc: dw_mmc: Cleanup disable of low power mode w/ SDIO interrupts

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Date:	Wed, 23 Oct 2013 20:25:36 +0900
From:	Seungwon Jeon <tgih.jun@...sung.com>
To:	'Doug Anderson' <dianders@...omium.org>,
	'Jaehoon Chung' <jh80.chung@...sung.com>
Cc:	'Chris Ball' <cjb@...top.org>,
	'James Hogan' <james.hogan@...tec.com>,
	'Grant Grundler' <grundler@...omium.org>,
	'Alim Akhtar' <alim.akhtar@...sung.com>,
	'Abhilash Kesavan' <a.kesavan@...sung.com>,
	'Tomasz Figa' <tomasz.figa@...il.com>,
	'Olof Johansson' <olof@...om.net>,
	'Sonny Rao' <sonnyrao@...omium.org>,
	'Bing Zhao' <bzhao@...vell.com>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: RE: [PATCH 1/2] mmc: dw_mmc: Cleanup disable of low power mode w/ SDIO
 interrupts

Hi Doug,

This change looks good.
There's comment below.

On Sat, October 19, 2013, Doug Anderson wrote:
> Jaehoon,
> 
> On Fri, Oct 18, 2013 at 2:42 AM, Jaehoon Chung <jh80.chung@...sung.com> wrote:
> >> -     clk_en_a = mci_readl(host, CLKENA);
> >> +     /*
> >> +      * Low power mode will stop the card clock when idle.  According to the
> >> +      * description of the CLKENA register we should disable low power mode
> >> +      * for SDIO cards if we need SDIO interrupts to work.
> >> +      */
> >> +     if (mmc->caps | MMC_CAP_SDIO_IRQ) {
> > mmc->caps & MMC_CAP_SDIO_IRQ?
> 
> Wow, that was an embarrassing one.  Thanks.
> 
> >> +             const u32 clken_low_pwr = SDMMC_CLKEN_LOW_PWR << slot->id;
> >> +             u32 clk_en_a_old;
> >> +             u32 clk_en_a;
> >>
> >> -     if (clk_en_a & clken_low_pwr) {
> >> -             mci_writel(host, CLKENA, clk_en_a & ~clken_low_pwr);
> >> -             mci_send_cmd(slot, SDMMC_CMD_UPD_CLK |
> >> -                          SDMMC_CMD_PRV_DAT_WAIT, 0);
> >> +             clk_en_a_old = mci_readl(host, CLKENA);
> >> +
> >> +             if (card->type == MMC_TYPE_SDIO ||
> >> +                 card->type == MMC_TYPE_SD_COMBO) {
&& card->quirks & MMC_QUIRK_BROKEN_CLK_GATING
How about considering MMC_QUIRK_BROKEN_CLK_GATING?
Some sdio device can work with gating clock.
For this, mmc_fixup_device() should be called prior to init_card() in core(sdio.c).
I guess you found that.

Thanks,
Seungwon Jeon

> >> +                     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);
> >> +                     clk_en_a = clk_en_a_old | clken_low_pwr;
> > When this condition is entered? card->type is always MMC_TYPE_SDIO or MMC_TYPE_SD_COMBO, isn't?
> 
> Ugh, that's not intuitive.  This callback is only called for SDIO
> cards and not MMC/SD cards?  That means if you plug in an SDIO card
> and then eject it and plug in an SD card you won't get to low power.
> Hrm.
> 
> I dug around a bit and couldn't find a better way to do this and then
> I realized that the other user of the init_card() callback has the
> same bug, so for the next version of the series I'm proposing a fix
> for mmc core to add this for all types.  If you have a better
> suggestion, I'm all ears.
> 
> -Doug
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