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

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Message-id: <001801ce9504$d9976ab0$8cc64010$%jun@samsung.com>
Date:	Fri, 09 Aug 2013 22:32:10 +0900
From:	Seungwon Jeon <tgih.jun@...sung.com>
To:	'Doug Anderson' <dianders@...omium.org>,
	'Chris Ball' <cjb@...top.org>
Cc:	'Olof Johansson' <olof@...om.net>,
	'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>,
	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 Wed, August 07, 2013, 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.
This mismatch comes only in case MMC_PM_KEEP_POWER, right?

> 
> 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.
I understand this change although some part of commit message (boot time, probe time...) make me confused.
I guess this change intends to update clock programming forcedly.
It looks like another version of 'dw_mci_setup_bus(slot, true)'.
Eventually, this change does same?

Thanks,
Seungwon Jeon

> 
> 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);
> --
> 1.8.3
> 
> --
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