linux-kernel - Re: [PATCH v5 3/4] mmc: dw_mmc: Cleanup disable of low power mode w/ SDIO interrupts

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Date:	Tue, 2 Dec 2014 17:12:20 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Jaehoon Chung <jh80.chung@...sung.com>
Cc:	Seungwon Jeon <tgih.jun@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Chris Ball <chris@...ntf.net>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/4] mmc: dw_mmc: Cleanup disable of low power mode w/
 SDIO interrupts

Jaehoon,

On Tue, Dec 2, 2014 at 5:06 PM, Jaehoon Chung <jh80.chung@...sung.com> wrote:
> Hi Doug
>
> On 12/03/2014 09:36 AM, Doug Anderson wrote:
>> Jaehoon,
>>
>> On Tue, Dec 2, 2014 at 4:17 PM, Jaehoon Chung <jh80.chung@...sung.com> wrote:
>>>> @@ -1245,27 +1246,37 @@ static int dw_mci_get_cd(struct mmc_host *mmc)
>>>>       return present;
>>>>  }
>>>>
>>>> -/*
>>>> - * Disable lower power mode.
>>>> - *
>>>> - * 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.
>>>> - *
>>>> - * This function is fast if low power mode is already disabled.
>>>> - */
>>>> -static void dw_mci_disable_low_power(struct dw_mci_slot *slot)
>>>> +static void dw_mci_init_card(struct mmc_host *mmc, struct mmc_card *card)
>>>>  {
>>>> +     struct dw_mci_slot *slot = mmc_priv(mmc);
>>>>       struct dw_mci *host = slot->host;
>>>> -     u32 clk_en_a;
>>>> -     const u32 clken_low_pwr = SDMMC_CLKEN_LOW_PWR << slot->id;
>>>>
>>>> -     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) {
>>>> +             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) {
>>>> +                     set_bit(DW_MMC_CARD_NO_LOW_PWR, &slot->flags);
>>>> +                     clk_en_a = clk_en_a_old & ~clken_low_pwr;
>>>> +             } else {
>>>
>>> I wonder this point. When entered at this point?
>>>
>>> MMC_CAP_SDIO_IRQ is sdio capability. and card->type is also related with SDIO, isn't?
>>
>> Right.  As I understand it:
>>
>> * You can certainly add MMC_CAP_SDIO_IRQ to an external card slot that
>> might have an MMC card, and SD card, or an SDIO card.  You still want
>> the LOW_PWR mode for MMC/SD cards but don't want it for SDIO cards in
>> that case.
>
> Ok, I understood your purpose.
> Your mean is MMC_CAP_SIDO_IRQ can be set to MMC or SD...not only SDIO card.
> It's reasonable.
> But i think it doesn't need to set LOW_PWR_mode for SD/eMMC at here. it should be already set to Low-power mode.
> And SDIO case should not enter at here.

Are you sure?  What about if you plug in an SDIO card, then unplug it,
then plug in an SD card?

>> * If you don't set MMC_CAP_SDIO_IRQ then presumably you've got some
>> problem where the SDIO interrupt is broken on your board.  That means
>> you're using polling mode to find interrupts.  As I understand it that
>> would allow you to use LOW_PWR since you don't need to detect SDIO
>> interrupts.  I know on Marvell WiFi modules I tested this seemed to
>> work OK, but I doubt anyone is really running a production device in
>> this way.
>
> No, we needs to set MMC_CAP_SDIO_IRQ, if i didn't set to it, i will also see the problem.
> Since I knew which slot is used as SDIO card, i thought MMC_CAP_SDIO_IRQ is set for only sdio card.
> Then it would be check the twice whether card is SDIO or not.
>
> Actually, i didn't test WiFi module with this patch. but concept is not problem.

Yup, I think you were only thinking about the embedded case where you
know that an SDIO card will be plugged into the slot.  In the case
where you have an exposed slot it is certainly possible to expect
someone might plug in an SD card or an SDIO card.  ...or even a combo
card!

-Doug
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