Re: [PATCH] mmc: dw_mmc-k3: Fix DDR52 mode by setting required clock divisor

Shawn Lin
2018-04-03T11:31:24Z

On 2018/3/30 2:24, oscardagrach wrote:

Need at least one line commit body.

> Signed-off-by: oscardagrach <ryan@edited.us>
> ---
> drivers/mmc/host/dw_mmc-k3.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc-k3.c b/drivers/mmc/host/dw_mmc-k3.c
> index 89cdb3d533bb..efc546cb4db8 100644
> --- a/drivers/mmc/host/dw_mmc-k3.c
> +++ b/drivers/mmc/host/dw_mmc-k3.c
> @@ -194,8 +194,14 @@ static void dw_mci_hi6220_set_ios(struct dw_mci *host, struct mmc_ios *ios)
> int ret;
> unsigned int clock;
>
> - clock = (ios->clock <= 25000000) ? 25000000 : ios->clock;
> -
> + /* CLKDIV must be 1 for DDR52/8-bit mode */
> + if (ios->bus_width == MMC_BUS_WIDTH_8 &&
> + ios->timing == MMC_TIMING_MMC_DDR52) {
> + mci_writel(host, CLKDIV, 0x1);
> + clock = ios->clock;
> + } else {
> + clock = (ios->clock <= 25000000) ? 25000000 : ios->clock;
> + }

I undertand DDR52/8-bit need CLKDIV fixed 1, but shouldn't the following
change is more sensible?

if (ios->bus_width == MMC_BUS_WIDTH_8 && ios->timing ==
MMC_TIMING_MMC_DDR52)
clock = ios->clock * 2;
else
clock = (ios->clock <= 25000000) ? 25000000 : ios->clock;

The reason is ios->clock is 52MHz and you could claim 104MHz from the
clock provider and let dw_mmc core take care of the divder to be 1.
Otherwise, you just force it to be DDR52/8-bit with a clk rate of 26MHz.

> ret = clk_set_rate(host->biu_clk, clock);
> if (ret)
> dev_warn(host->dev, "failed to set rate %uHz\n", clock);
>