linux-kernel - RE: [PATCH v6 2/3] mmc: dw_mmc: Honor requests to set the clock to 0 (turn off clock)

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Message-id: <001201cea215$8c125e30$a4371a90$%jun@samsung.com>
Date:	Mon, 26 Aug 2013 13:34:26 +0900
From:	Seungwon Jeon <tgih.jun@...sung.com>
To:	'Doug Anderson' <dianders@...omium.org>,
	'Chris Ball' <cjb@...top.org>
Cc:	'Jaehoon Chung' <jh80.chung@...sung.com>,
	'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>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: RE: [PATCH v6 2/3] mmc: dw_mmc: Honor requests to set the clock to 0
 (turn off clock)

On Fri, August 23, 2013, Doug Anderson wrote:
> Previously the dw_mmc driver would ignore any requests to disable the
> card's clock.  This doesn't seem like a good thing in general, but had
> one extra bad side effect in the following situtation:
> * mmc core would set clk to 400kHz at boot time while initting
> * mmc core would set clk to 0 since no card, but it would be ignored.
> * suspend to ram and resume; clocks in the dw_mmc IP block are now 0
>   but dw_mmc thinks that they're 400kHz (it ignored the set to 0).
> * insert card
> * mmc core would set clk to 400kHz which would be considered a no-op.
> 
> Note that if there is no card in the slot and we do a suspend/resume
> cycle, we _do_ still end up with differences in a dw_mmc register
> dump, but the differences are clock related and we've got the clock
> disabled both before and after, so this should be OK.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
> Changes in v6:
> - Replaces previous pathes that ensured saving/restoring clocks.
> 
>  drivers/mmc/host/dw_mmc.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index ee5f167..f6c7545 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -635,7 +635,11 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>  	u32 div;
>  	u32 clk_en_a;
> 
> -	if (slot->clock != host->current_speed || force_clkinit) {
> +	if (slot->clock == 0) {
> +		mci_writel(host, CLKENA, 0);
> +		mci_send_cmd(slot,
> +			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
Basically dw_mmc driver uses host's low power mode(auto clock gating)
So, how about keeping origin code rather than programming clock setting to '0'?
 
> +	} else if (slot->clock != host->current_speed || force_clkinit) {
And then, if condition('slot->clock is not zero') is added in order to allow to set clock,
print messages which Jaehoon pointed would be solved.

Thanks,
Seungwon Jeon

>  		div = host->bus_hz / slot->clock;
>  		if (host->bus_hz % slot->clock && host->bus_hz > slot->clock)
>  			/*
> @@ -675,9 +679,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>  		/* inform CIU */
>  		mci_send_cmd(slot,
>  			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
> -
> -		host->current_speed = slot->clock;
>  	}
> +	host->current_speed = slot->clock;
> 
>  	/* Set the current slot bus width */
>  	mci_writel(host, CTYPE, (slot->ctype << slot->id));
> @@ -807,13 +810,11 @@ static void dw_mci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> 
>  	mci_writel(slot->host, UHS_REG, regs);
> 
> -	if (ios->clock) {
> -		/*
> -		 * Use mirror of ios->clock to prevent race with mmc
> -		 * core ios update when finding the minimum.
> -		 */
> -		slot->clock = ios->clock;
> -	}
> +	/*
> +	 * Use mirror of ios->clock to prevent race with mmc
> +	 * core ios update when finding the minimum.
> +	 */
> +	slot->clock = ios->clock;
> 
>  	if (drv_data && drv_data->set_ios)
>  		drv_data->set_ios(slot->host, ios);
> --
> 1.8.3
> 
> --
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