linux-kernel - Re: [RFC v2 2/2] sdhci: Prevent SD from doing high-speed timing when broken-highspeed property is set

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Message-ID: <58380ee1-15d0-9eb6-fe89-f1bb9ec24af2@intel.com>
Date:   Mon, 17 Oct 2016 09:56:19 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Zach Brown <zach.brown@...com>, ulf.hansson@...aro.org
Cc:     robh+dt@...nel.org, mark.rutland@....com,
        linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 2/2] sdhci: Prevent SD from doing high-speed timing when
 broken-highspeed property is set

On 12/10/16 21:40, Zach Brown wrote:
> When the broken-highspeed property is set the sdhci driver will not
> go into highspeed mode even if the controller and card appear to
> otherwise support highspeed mode.
> 
> This is useful in cases where the controller and card support highspeed,
> but the board configuration or some other issue make highspeed
> impossible. For example, we send the SDIO lines through a fpga so we
> need the data to change on the falling edge of the clock or there will
> be issues with hold time.
> 
> Signed-off-by: Zach Brown <zach.brown@...com>

Assuming the DT property is accepted:

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
>  drivers/mmc/host/sdhci.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 4805566..17e6c50 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -22,6 +22,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/of.h>
>  
>  #include <linux/leds.h>
>  
> @@ -3274,7 +3275,8 @@ int sdhci_setup_host(struct sdhci_host *host)
>  	if (host->quirks2 & SDHCI_QUIRK2_HOST_NO_CMD23)
>  		mmc->caps &= ~MMC_CAP_CMD23;
>  
> -	if (host->caps & SDHCI_CAN_DO_HISPD)
> +	if ((host->caps & SDHCI_CAN_DO_HISPD) &&
> +	    !(of_property_read_bool(mmc_dev(mmc)->of_node, "broken-highspeed")))
>  		mmc->caps |= MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED;
>  
>  	if ((host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION) &&
>