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 16:36:46 -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 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.

* 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.


Basically I was trying to mirror the functionality of the old code as
closely as possible.  In the old code if you were using polling mode
then dw_mci_enable_sdio_irq() should never be called and you'd never
go out of low power mode.

-Doug
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