Re: [PATCH v3 1/13] mmc: sunxi: Fix clock frequency change sequence

Ulf Hansson
2017-01-24T08:12:07Z

On 16 January 2017 at 17:56, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> The MMC and SD specifications documents that the clock frequency should
> only be changed once gated.

Where?

>
> The current code first modifies the parent clock, gates it and then
> modifies the internal divider. This means that since the parent clock rate
> might be changed, the bus clock might be changed as well before it is
> gated, which breaks the specification.
>
> Move the gating before the parent rate modification.

This all makes perfect sense to me, however I am not sure you need to
refer to the spec to justify these changes.

Kind regards
Uffe

>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
> drivers/mmc/host/sunxi-mmc.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
> index b1d1303389a7..ab4324e6eb74 100644
> --- a/drivers/mmc/host/sunxi-mmc.c
> +++ b/drivers/mmc/host/sunxi-mmc.c
> @@ -761,6 +761,10 @@ static int sunxi_mmc_clk_set_rate(struct sunxi_mmc_host *host,
> u32 rval, clock = ios->clock;
> int ret;
>
> + ret = sunxi_mmc_oclk_onoff(host, 0);
> + if (ret)
> + return ret;
> +
> /* 8 bit DDR requires a higher module clock */
> if (ios->timing == MMC_TIMING_MMC_DDR52 &&
> ios->bus_width == MMC_BUS_WIDTH_8)
> @@ -783,10 +787,6 @@ static int sunxi_mmc_clk_set_rate(struct sunxi_mmc_host *host,
> return ret;
> }
>
> - ret = sunxi_mmc_oclk_onoff(host, 0);
> - if (ret)
> - return ret;
> -
> /* clear internal divider */
> rval = mmc_readl(host, REG_CLKCR);
> rval &= ~0xff;
> --
> git-series 0.8.11