On 7 October 2014 10:11, Ludovic Desroches <ludovic.desroches@xxxxxxxxx> wrote:
> In programmable mode, if the clock frequency is too high, the divider
> can be too small to meet the clock frequency requirement especially to
> init the SD card. In this case, switch to the divided clock mode.
>
> Signed-off-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxx>
> ---
>
> Hi all,
>
> I would like to know if this patch can be accepted. Use case, I have a base
> clock at 12 MHz, M is 40. So in programmable mode, using the greater divider,
> minimum clock frequency will be higher than 400 KHz so it could cause issues to
> init the card.
>
> Thanks for your feedback.
>
> Ludovic
It would be nice if some of the senior sdhci developers could help out
review patches likes this.
It touches the core of sdhci, thus affecting many of the sdhci drivers.
Anybody?
Kind regards
Uffe
>
> drivers/mmc/host/sdhci.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index df0e7e1..70d4c18 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1126,6 +1126,7 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
> int real_div = div, clk_mul = 1;
> u16 clk = 0;
> unsigned long timeout;
> + bool switch_base_clk = false;
>
> host->mmc->actual_clock = 0;
>
> @@ -1163,15 +1164,25 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
> <= clock)
> break;
> }
> - /*
> - * Set Programmable Clock Mode in the Clock
> - * Control register.
> - */
> - clk = SDHCI_PROG_CLOCK_MODE;
> - real_div = div;
> - clk_mul = host->clk_mul;
> - div--;
> - } else {
> + if ((host->max_clk * host->clk_mul / div) <= clock) {
> + /*
> + * Set Programmable Clock Mode in the Clock
> + * Control register.
> + */
> + clk = SDHCI_PROG_CLOCK_MODE;
> + real_div = div;
> + clk_mul = host->clk_mul;
> + div--;
> + } else {
> + /*
> + * Divisor can be too small to reach clock
> + * speed requirement. Then use the base clock.
> + */
> + switch_base_clk = true;
> + }
> + }
> +
> + if (!host->clk_mul || switch_base_clk) {
> /* Version 3.00 divisors must be a multiple of 2. */
> if (host->max_clk <= clock)
> div = 1;
> --
> 2.0.3
>
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