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

Shawn Lin
2018-04-05T00:51:14Z

[+ Zhangfei Gao who added support for hi6220]

On 2018/4/4 23:31, Ryan Grachek wrote:
> On Tue, Apr 3, 2018 at 6:31 AM, Shawn Lin <shawn.lin@rock-chips.com
> <mailto:shawn.lin@rock-chips.com>> wrote:
>
> On 2018/3/30 2:24, oscardagrach wrote:
>
> Need at least one line commit body.
>
> Signed-off-by: oscardagrach <ryan@edited.us <mailto: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);
>
>
>

For future wise, please use plain mode mail, but not HTML format.

> Your feedback is correct. I see the Rockchip dwmmc driver has a similar
> implementation. After applying your suggested changes, however, my board
> reports "dwmmc_k3 f723d000.dwmmc0: failed to set rate 104000000Hz"
> during intialization of eMMC. In addition, I do not see CLKDIV being
> set to 1. clk_set_rate fails and I wonder if this is out-of-scope of
> the driver.
>
> If I set CLKDIV where I did prior, with your changes, the device fails
> to set the clock and falls back to 52 MHz (26 MHz) and works fine, but
> again, CLKDIV is reported as 0 (even though it is 1.) One thing of
> interest to note is when I manually set the clock by doing:
> (echo 104000000 > /sys/kernel/debug/mmc0/clock) the device reports back
> 'mmc_host mmc0: Bus speed (slot 0) = 198400000Hz (slot req 104000000Hz,
>  actual 99200000HZ div = 1)' which works reliably and clk_set_rate does
> not report any error.
>

When looking closely into the code, at least dw_mci_hi6220_set_ios
goes wrong with the bus_hz, since it should be ciu_clk but not biu_clk.
"b" stands for bus, and "c" stands for card IMHO, however bus_hz
describs the clock to the card, provided by controller. Does the
following patch help?

diff --git a/drivers/mmc/host/dw_mmc-k3.c b/drivers/mmc/host/dw_mmc-k3.c
index 89cdb3d..9e78cf2 100644
--- a/drivers/mmc/host/dw_mmc-k3.c
+++ b/drivers/mmc/host/dw_mmc-k3.c
@@ -194,13 +194,21 @@ 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;
+ 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;

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

- host->bus_hz = clk_get_rate(host->biu_clk);
+ clock = clk_get_rate(host->ciu_clk);
+ if (clock != host->bus_hz) {
+ host->bus_hz = clock;
+ host->current_speed = 0;
+ }
}

> I am not sure where to begin debugging these clock issues and welcome
> any feedback.