[U-Boot] [RFC] mmc:fix: Increase the timeout value for SDHCI_send_command()

[Lukasz Majewski <l.majewski@samsung.com>]

Hi Wolfgang,

> Dear Lukasz Majewski,
> 
> In message <1357665792-8141-1-git-send-email-l.majewski@samsung.com>
> you wrote:
> > I'd like to ask for your opinion about the following problem:
> 
> I cannot comment on the problem - only a bit about the proposed patch
> ;-)
> 
> > From a brief checking I can say that it happens when we are doing
> > consecutive MMC operations (i.e. many reads), and the 10ms timeout
> > might be too short when eMMC firmware is forced to do some internal
> > time consuming operations (e.g. flash blocks management, wear
> > leveling).
> > In this situation, the SDHCI_CMD_INHIBIT bit is set, which means
> > that SDHCI controller didn't received response from eMMC.
> > 
> > One proposition would be to define the per device/per memory chip
> > specific timeouts, to replace those defined at ./drivers/mmc/sdhci.c
> > file.
> 
> Is there no way to ask the device and/or controller when it is done,
> so we can poll for ready state instead of adding delays, which will
> always have to be tailored for the so far known worst case, i. e. they
> will be always too long on all almost all systems.

We are doing this already - the SDHCI_PRESENT_STATE register's bit 0
(SDHCI_CMD_INHIBIT) and bit 1 (DATA_INHIBIT) are for this purpose.
Those indicate when host controller can send further command/data to
the card.

Moreover, there are also timeouts in the case when someone pull out SD
card inserted to the slot (or any other use case which I'm not aware).


> 
> > --- a/drivers/mmc/sdhci.c
> > +++ b/drivers/mmc/sdhci.c
> > @@ -137,8 +137,8 @@ int sdhci_send_command(struct mmc *mmc, struct
> > mmc_cmd *cmd, unsigned int timeout, start_addr = 0;
> >  	unsigned int retry = 10000;
> >  
> > -	/* Wait max 10 ms */
> > -	timeout = 10;
> > +	/* Wait max 100 ms */
> > +	timeout = 100;
> 
> We have cases where we struggle for sub-second boot times.  Adding
> 100 ms delay here is clearly prohbitive.  [Even the 10 ms are way too
> long IMHO.]  There must be a better way to handle this.

That's why I'm asking. 

It is strange that, when I'm increasing delay it works.

Maybe we will find some areas of optimization?

> 
> Best regards,
> 
> Wolfgang Denk
> 



-- 
Best regards,

Lukasz Majewski

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