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SubjectRe: [PATCH v3] mmc: Make ID freq configurable
On 01/02/2010 04:23 PM, Ben Nizette wrote:
>
> On 02/01/2010, at 11:08 PM, Pierre Ossman wrote:
>
>> On Sat, 2 Jan 2010 20:07:01 +1100
>> Ben Nizette<bn@niasdigital.com> wrote:
>>
>>>
>>> Pierre, thoughts? All my cards were borderline spec but Hein's got a mainstream, common card which seems to completely ignore the spec. Can we just take the few-hundred-uS hit and allow initialization down at the bottom end, say 100kHz?
>>>
>>
>> Broken cards seem to be all over the spectrum, so I wouldn't be
>> suprised if you find ones that break if you go too low as well.
>
> Yea good point, though given there might not even be a One Freq to Rule Them All, how about:
>
> ---8<---
>
> From: Ben Nizette<bn@niasdigital.com>
> Subject: [PATCH v3] mmc: Make ID freq configurable
>
> While the SD spec specifies a range of frequencies for the ID phase from 100-400kHz, not all cards play by the rules. This patch adds a Kconfig option to allow the user to tweak this to their card/host config, though the default of 250kHz should be fine for all spec-abiding cards and most others besides.
>
> Signed-off-by: Ben Nizette<bn@niasdigital.com>
>
> ---
> diff --git a/drivers/mmc/core/Kconfig b/drivers/mmc/core/Kconfig
> index ab37a6d..a8e5003 100644
> --- a/drivers/mmc/core/Kconfig
> +++ b/drivers/mmc/core/Kconfig
> @@ -14,3 +14,15 @@ config MMC_UNSAFE_RESUME
> This option is usually just for embedded systems which use
> a MMC/SD card for rootfs. Most people should say N here.
>
> +config MMC_ID_FREQ
> + int "SD/MMC Card initialisation frequency (Hz)"
> + default 250000
> + help
> + The SD card specification allows for initialisation
> + frequencies from 100-400kHz however some broken cards are
> + known not to work across this whole range.
> +
> + If you're having problems with a particular card not being
> + detected, you may try adjusting this frequency up or down
> + but for widest compatibility just leave it default.

Don't know that a kconfig option is best for this, it'd suck to have to
recompile the kernel to change it. Module option might be better..


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