linux-kernel - Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock

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Date:	Thu, 5 Nov 2015 17:42:16 -0800
From:	Bjorn Andersson <bjorn@...o.se>
To:	"Ivan T. Ivanov" <ivan.ivanov@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Georgi Djakov <georgi.djakov@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Peter Griffin <peter.griffin@...aro.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock

On Mon, Jul 6, 2015 at 4:53 AM, Ivan T. Ivanov <ivan.ivanov@...aro.org> wrote:
> Ensure SDCC is working with maximum clock otherwise card
> detection could be extremely slow, up to 7 seconds.
>
> Signed-off-by: Ivan T. Ivanov <ivan.ivanov@...aro.org>
> Reviewed-by: Georgi Djakov <georgi.djakov@...aro.org>
> Acked-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
>
> Changes since v0:
> - s/falied/failed in warning message.
>
>  drivers/mmc/host/sdhci-msm.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> index 4a09f76..4bcee03 100644
> --- a/drivers/mmc/host/sdhci-msm.c
> +++ b/drivers/mmc/host/sdhci-msm.c
> @@ -489,6 +489,11 @@ static int sdhci_msm_probe(struct platform_device *pdev)
>                 goto pclk_disable;
>         }
>
> +       /* Vote for maximum clock rate for maximum performance */
> +       ret = clk_set_rate(msm_host->clk, INT_MAX);
> +       if (ret)
> +               dev_warn(&pdev->dev, "core clock boost failed\n");
> +

On my 8974AC devices this results in GCC_SDCC1_APPS_CLK changing from
100MHz to 200MHz for my eMMC. Unfortunately this results in the
following error:

[    5.103241] mmcblk0: retrying because a re-tune was needed
[    5.109270] mmcblk0: error -84 transferring data, sector 5816322,
nr 2, cmd response 0x900, card status 0xc00

Looking at the board specification it's stated that these card should
run in DDR50, so I've tried specifying "max-frequency" in the dt. I
verified in sdhci_set_clock() that we get a divisor of 4, but the
result is a repetition of:

[    1.702312] mmc1: Switching to 3.3V signalling voltage failed
[    1.837987] mmc1: power class selection to bus width 8 ddr 0 failed
[    1.846227] mmc1: error -110 whilst initialising MMC card
[    1.946303] mmc1: Reset 0x1 never completed.

I tried to disable HS200 by specifying SDHCI_QUIRK2_BROKEN_HS200. This
makes the card come up nicely again.


Is there any other way to force the link to DDR50? Is it acceptable to
expose the broken-hs200 quirk in dt so I can use that for now?

(The downstream fix used for this was apparently to just remove all
other caps...)

Regards,
Bjorn
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