[PATCH] mmc: mtk-sd: increase the minimum bus frequency

[Jaehoon Chung]

Dear Waijie,

On 3/5/21 11:30 AM, Weijie Gao wrote:
> With a 48MHz input clock, the lowest bus frequency can be as low as
> 48000000 / (4 * 4095) = 2930Hz. Such an extremely low frequency will cause
> the mmc framework take seconds to finish the initialization.
> 
> Limiting the minimum bus frequency to a slightly higher value can solve the
> issue without any side effects.
> 
> Signed-off-by: Weijie Gao <weijie.gao at mediatek.com>
> ---
>  drivers/mmc/mtk-sd.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/mmc/mtk-sd.c b/drivers/mmc/mtk-sd.c
> index 3b9c12266a..1e1726ef31 100644
> --- a/drivers/mmc/mtk-sd.c
> +++ b/drivers/mmc/mtk-sd.c
> @@ -232,6 +232,8 @@
>  
>  #define SCLK_CYCLES_SHIFT		20
>  
> +#define MIN_BUS_CLK			260000

Is there any reason to define 260KHz? 
According to specification, clock frequency should be chosen one of {100000, 200000, 300000, 400000}.

How about defined one of them?

Best Regards,
Jaehoon Chung

> +
>  #define CMD_INTS_MASK	\
>  	(MSDC_INT_CMDRDY | MSDC_INT_RSPCRCERR | MSDC_INT_CMDTMO)
>  
> @@ -1639,6 +1641,9 @@ static int msdc_drv_probe(struct udevice *dev)
>  	else
>  		cfg->f_min = host->src_clk_freq / (4 * 4095);
>  
> +	if (cfg->f_min < MIN_BUS_CLK)
> +		cfg->f_min = MIN_BUS_CLK;
> +
>  	cfg->f_max = host->src_clk_freq;
>  
>  	cfg->b_max = 1024;
>