linux-kernel - Re: [PATCH v4 1/4] mmc: dw_mmc: Invalidate cache of current

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Message-ID: <4496642.gd8AClQe6R@flatron>
Date:	Tue, 06 Aug 2013 23:58:49 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Chris Ball <cjb@...top.org>, Olof Johansson <olof@...om.net>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Seungwon Jeon <tgih.jun@...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>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] mmc: dw_mmc: Invalidate cache of current_speed after suspend/resume

On Tuesday 06 of August 2013 14:37:48 Doug Anderson wrote:
> The dw_mmc driver keeps a cache of the current slot->clock in order to
> avoid doing a whole lot of work every time set_ios() is called.
> However, after suspend/resume the register values are bogus so we need
> to ensure that the cached value is invalidated.
> 
> In many cases we got by without this since the core mmc code fiddles
> with the clock a lot.  If we've got a card present we're probably
> running it at something like 50MHz and the core will temporarily
> switch us to 400kHz after resume.  One case that didn't work (for me)
> is the case of having no card in the slot.  The slot is initted to
> 400kHz at boot time.  After suspend/resume the slot thinks it's still
> at 400kHz (due to the cache) so doesn't adjust timing.  When it tries
> to send the command at probe time it just times out and gets left in a
> bad state.
> 
> Invalidating the current_speed also means that we don't need to call:
>   dw_mci_setup_bus(slot, true);
> ...to force an update of the clock in the case when the slot was left
> powered.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
> Changes in v4: None
> Changes in v3: None
> Changes in v2:
> - Fix typo (some -> come)
> - Use ~0 instead of 0xFFFFFFFF; add comment about value
> 
>  drivers/mmc/host/dw_mmc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index ee5f167..13a363c 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -2511,13 +2511,19 @@ int dw_mci_resume(struct dw_mci *host)
>  		   DW_MCI_ERROR_FLAGS | SDMMC_INT_CD);
>  	mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
> 
> +	/*
> +	 * Invalidate the 'current_speed' value since CLKDIV has come up 
in
> +	 * default state and our cache is incorrect; set to something we 
know
> +	 * slot->clock won't be.
> +	 */
> +	host->current_speed = ~0;
> +
>  	for (i = 0; i < host->num_slots; i++) {
>  		struct dw_mci_slot *slot = host->slot[i];
>  		if (!slot)
>  			continue;
>  		if (slot->mmc->pm_flags & MMC_PM_KEEP_POWER) {
>  			dw_mci_set_ios(slot->mmc, &slot->mmc->ios);
> -			dw_mci_setup_bus(slot, true);
>  		}
> 
>  		ret = mmc_resume_host(host->slot[i]->mmc);

Reviewed-by: Tomasz Figa <t.figa@...sung.com>

Best regards,
Tomasz

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