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

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Date:	Wed, 03 Dec 2014 10:19:06 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Doug Anderson <dianders@...omium.org>
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

Doug.

On 12/03/2014 10:12 AM, Doug Anderson wrote:
> 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?

Oh.. :) I missed this case. thank you for pointing out.
I considered only non-removable case, it's stupid...

Best Regards,
Jaehoon Chung

> 
>>> * 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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