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

[Ryan Grachek <ryan@edited.us>]

On Wed, Apr 4, 2018 at 7:51 PM, Shawn Lin <shawn.lin@rock-chips.com> wrote:
> [+ 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.
>
>

The change results in the following:
'dwmmc_k3 f723e000.dwmmc1: failed to set rate 25000000Hz'
'dwmmc_k3 f723d000.dwmmc0: failed to set rate 25000000Hz'
'dwmmc_k3 f723f000.dwmmc2: failed to set rate 25000000Hz'

and later on:
'dwmmc_k3 f723d000.dwmmc0: failed to set rate 52000000Hz'
'dwmmc_k3 f723d000.dwmmc0: failed to set rate 104000000Hz'

Eventually mmc1 (UHS-1 MicroSD) will settle down after repeated
attempts at setting 25 MHz:
'mmc_host mmc1: Bus speed (slot 0) = 100000000Hz (slot req
100000000Hz, actual 100000000HZ div = 0)'
'mmc1: new ultra high speed SDR50 SDHC card at address 0001'
'mmcblk1: mmc1:0001 GB1QT 29.8 GiB'

Same for mmc2 (SDIO WL1835MOD WiFi):
'mmc_host mmc2: Bus speed (slot 0) = 100000000Hz (slot req 50000000Hz,
actual 50000000HZ div = 1)'
'mmc2: new high speed SDIO card at address 0001'

So mmc1 and mmc2 will initialize eventually. I had not observed this
behavior prior. It appears to fail setting
all devices to an initial rate of 25 MHz. However, the same cannot be
said for mmc0 (eMMC).
Again, I observed being able to set the clock manually through debugfs
to 104MHz(/2) which is successful
and the card becomes stable and will initialize properly.

'echo 104000000 > /sys/kernel/debug/mmc0/clock'
'mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req
104000000Hz, actual 100000000HZ div = 1)'

So it seems to settle down at 50 MHz, but only if set manually. It
does appear CLKDIV is being set accordingly now.