Re: [PATCH] mmc: sh_mmcif: mmc->f_max heuristic

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Hi Simon

Thanks for addressing this issue.

On Wed, 20 Jun 2012, Simon Horman wrote:

> In 930f152cc9998388031af577843baae572ac8ab6 ("mmc: sh_mmcif: mmc->f_max
> should be half of the bus clock") I changed the setting of mmc->f_max from
> the bus clock to half the bus clock based on the manual for the sh7372 SoC.
> 
> Inspection of sh_mmcif_clock_control() reveals that it relies on
> mmc->f_max being set to the bus speed in order to enable the supplementary
> clock, a feature that does not exist on the sh7372.
> 
> Armed with this information implement the following heuristic for setting
> mmc->f_max:
> 
> * Use bus clock if the supplementary clock feature is present
>   - Assumed to work on the sh7757lcr board, the only board present
>     in the tree which has the feature.

To be able to better understand this change: do we have access to the 
sh7757 documentation and does it actually explain how the CLK_SUP_PCLK bit 
in MMCIF_CE_CLK_CTRL functions? Does it actually set the MMC bus clock to 
be equal to the host clock?

Thanks
Guennadi

> * Use half the bus clock otherwise
>   - As per the documentation for the sh7372 SoC.
> 
> Reported-by: Magnus Damm <damm@xxxxxxxxxxxxx>
> Cc: Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
> Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
> 
> ---
> 
> Regression information:
> 
> It seems likely that this resolves a regression for the sh7757lcr which was
> introduced by 930f152cc9998388031af577843baae572ac8ab6 ("mmc: sh_mmcif:
> mmc->f_max should be half of the bus clock"). However, although I have the
> hardware in question I am unsure how to exercise the code to test if there
> is a problem or not.
> 
> 930f152cc9998388031af577843baae572ac8ab6 was added between the 3.3 and 3.4.
> 
> Dependency information:
> 
> This patch is based on Guennadi Liakhovetski's recent series
> "[PATCH 0/5 v4] mmc: sh_mmcif: clock and power updates". It should
> be trivial to rebase it on 3.5-rc3.
> ---
>  drivers/mmc/host/sh_mmcif.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sh_mmcif.c b/drivers/mmc/host/sh_mmcif.c
> index f0f518b..dfcfe83 100644
> --- a/drivers/mmc/host/sh_mmcif.c
> +++ b/drivers/mmc/host/sh_mmcif.c
> @@ -919,10 +919,11 @@ static void sh_mmcif_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  static int sh_mmcif_clk_update(struct sh_mmcif_host *host)
>  {
>  	int ret = clk_enable(host->hclk);
> +	struct sh_mmcif_plat_data *p = host->pd->dev.platform_data;
>  
>  	if (!ret) {
>  		host->clk = clk_get_rate(host->hclk);
> -		host->mmc->f_max = host->clk / 2;
> +		host->mmc->f_max = p->sup_pclk ? host->clk : host->clk / 2;
>  		host->mmc->f_min = host->clk / 512;
>  	}
>  
> -- 
> 1.7.10.2.484.gcd07cc5
> 

---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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