[PATCH 1/4] mmc: mediatek: Add online-tuning support of EMMC/SD

[Ulf Hansson]

On 17 August 2015 at 14:01, Chaotian Jing <chaotian.jing at mediatek.com> wrote:
> Hi Ulf,
> Thanks, please see my comment:
> On Mon, 2015-08-17 at 13:31 +0200, Ulf Hansson wrote:
>> On 12 August 2015 at 10:24, Chaotian Jing <chaotian.jing at mediatek.com> wrote:
>> > Schedule a workqueue to do tuning when CRC error
>> > Call mmc_hw_reset to re-init card when data timeout
>>
>> Thanks to Adrian Hunter, the mmc core already supports re-tuning for
>> the above scenarios through the mmc_retune_*() APIs.
>>
>> SDHCI driver has already adopted to use that feature, you should do
>> that for the mtk-sd driver as well.
>>
>> Kind regards
>> Uffe
>>
> I also noticed that the mmc core already supports re-tuning, but it is
> not suitable for our host.
> For EMMC, the CMD21 only support HS200/HS400 mode, for SD card, CMD19
> only support SDR50/SDR104 mode, but in our host, even 50Mhz clock
> frequency may also occur CRC error, Cannot find a parameter that can
> cover all SD cards which running at 50Mhz, even 25Mhz, will occur CRC
> error for stress test, DDR50 mode is worse.

I don't follow. You may run for example HS200 in lower speed, nothing
will prevent tuning and re-tuning from happen for these scenarios.

Or you are talking about other speed modes than HS200/400 and
SDR50/104? If so, which speed modes are these?

BTW, there are currently a patch being discussed which is about adding
tuning for DDR mode. Please have look.
http://www.spinics.net/lists/arm-kernel/msg438434.html

Regarding re-tuning on CRC errors, that's already supported by the mmc
core. More precisely when a host driver returns -EILSEQ for a request.

> By the way,there are too many tune parameters need try for response,
> read data, write crc status CRC error, these parameters are
> multidimensional, it is hard to find a best parameter, and, try
> thousands of parameters will take long time.

As I see, it's your responsibility from the host driver to propagate
the proper error code towards the mmc core. If you encounter an error
that you want to trigger a retune, just return -EILSEQ.

Moreover, if you see a need to extend the tuning/re-tuning support in
the mmc core to suit your need - I am definitely open to look into
that. More importantly, I don't want to see host specific hacks trying
to deal with this.

Kind regards
Uffe