linux-kernel - Re: [RFC v2 1/2] sdhci: Add device tree property broken-highspeed

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Date:   Thu, 13 Oct 2016 11:27:23 +0900
From:   Jaehoon Chung <jh80.chung@...sung.com>
To:     Zach Brown <zach.brown@...com>, ulf.hansson@...aro.org
Cc:     adrian.hunter@...el.com, 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 1/2] sdhci: Add device tree property broken-highspeed

On 10/13/2016 03:40 AM, Zach Brown wrote:
> Certain board configurations can make highspeed malfuction due to timing
> issues. In these cases a way is needed to force the controller and card
> into standard speed even if they otherwise appear to be capable of
> highspeed.

I'm not sure "broken-hishspeed" property is relevant to only sdhci driver? otherwise on card side..?
Subject looks like only sdhci driver..And your RFC patch should be supported only SDHCI driver.
But your [patch 1/2] can cause the confusing in future..because there are just comment as "controller".

Then developer who refer to mmc.txt will add the property "broken-highspeed".
I'm not sure what is correct way..but to prevent confusing..you mentioned only "sdhci" driver or supporting other controller.

Best Regards,
Jaehoon Chung

> 
> The broken-highspeed property will let the sdhci driver know that
> highspeed will not work.
> 
> Signed-off-by: Zach Brown <zach.brown@...com>
> ---
>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> index 8a37782..a2b298c 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> @@ -52,6 +52,8 @@ Optional properties:
>  - no-sdio: controller is limited to send sdio cmd during initialization
>  - no-sd: controller is limited to send sd cmd during initialization
>  - no-mmc: controller is limited to send mmc cmd during initialization
> +- broken-highspeed: Highspeed is broken, even if the controller and card
> +  themselves claim they support highspeed.
>  
>  *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
>  polarity properties, we have to fix the meaning of the "normal" and "inverted"
>