[PATCH v3 1/4] mmc: dw_mmc: exynos: incorporate ciu_div into timing property

[Alim Akhtar]

Hi Doug,
Thanks for looking into this series.

On Fri, Jan 2, 2015 at 10:28 PM, Doug Anderson <dianders at chromium.org> wrote:
> Alim,
>
> On Tue, Dec 30, 2014 at 10:43 PM, Alim Akhtar <alim.akhtar at samsung.com> wrote:
>> From: Seungwon Jeon <tgih.jun at samsung.com>
>>
>> ciu_div may not be common value for all speed mode.
>> So, it needs to be attached to CLKSEL timing.
>
> The more time I've spent looking at all of this stuff the less I like
> the exynos bindings.  Personally I'd prefer to see the exynos bindings
> fixed rather than go further down the path of these bindings.
>
> Specifically:
>
> 1. The "drive" really should be specified quite differently.
> According to the DesignWare docs, the "drive" phase is there to meet
> hold time requirements.  Hold time requirements are different for
> different SD/MMC modes and are specified in nanoseconds (SDR104 is
> .8ns, ID mode is 5.0ns).  There is a per-SoC parameter needed that
> indicates some built-in delay (in nanoseconds) and that shouldn't
> change based on clock speed or card mode.
>
Yes, "drive" phase shift are there to meet hold time requirements. And
that why we in general don't change it as those are fixed for a
SoC/Board based on actual measurement of the same.

> 2. The ciu_div really ought to be automatic.  Start out at a divide by
> 4.  If you end up with both drive and sample at phases of 0, 90, 180,
> 270 then you can change to divide by 2.
>
> I still haven't looked at every last detail of these delays though, so
> please correct me if I'm wrong.  I've added Alex who may have looked
> at this more than I have.
>
Thanks, suggestions/comments are welcome.
>
> With all of the above, there's also the fact that (I think) we should
> be moving towards working with the clock phase API since all of your
> values are effectively specifying clock phases, just in a very arcane
> way.
>
That is something nice to have, and should be done at some point.
As you know exynos implements a custom register called CLKSEL, and it
allows us to set the required "sample" phase shift. And exynos uses
"variable delay tuning" as per DW databook to set "sample" phase shift
based on tuning data.
>
>> This also introduce a new compatibale 'dw-mshc-hs200-timing'
>> for selecting hs200 timing value
>
> As per above, I don't think this is needed.
>
>
>> Signed-off-by: Seungwon Jeon <tgih.jun at samsung.com>
>> Signed-off-by: Alim Akhtar <alim.akhtar at samsung.com>
>> ---
>>  .../devicetree/bindings/mmc/exynos-dw-mshc.txt     |   15 ++--
>>  drivers/mmc/host/dw_mmc-exynos.c                   |   81 ++++++++++++++------
>>  drivers/mmc/host/dw_mmc-exynos.h                   |    1 +
>>  3 files changed, 67 insertions(+), 30 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt b/Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt
>> index ee4fc05..06455de 100644
>> --- a/Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt
>> +++ b/Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt
>> @@ -23,10 +23,6 @@ Required Properties:
>>         - "samsung,exynos7-dw-mshc-smu": for controllers with Samsung Exynos7
>>           specific extensions having an SMU.
>>
>> -* samsung,dw-mshc-ciu-div: Specifies the divider value for the card interface
>> -  unit (ciu) clock. This property is applicable only for Exynos5 SoC's and
>> -  ignored for Exynos4 SoC's. The valid range of divider value is 0 to 7.
>> -
>>  * samsung,dw-mshc-sdr-timing: Specifies the value of CIU clock phase shift value
>>    in transmit mode and CIU clock phase shift value in receive mode for single
>>    data rate mode operation. Refer notes below for the order of the cells and the
>> @@ -37,11 +33,16 @@ Required Properties:
>>    data rate mode operation. Refer notes below for the order of the cells and the
>>    valid values.
>>
>> +* samsung,dw-mshc-hs200-timing: Similar with dw-mshc-sdr-timing.
>> +
>>    Notes for the sdr-timing and ddr-timing values:
>>
>>      The order of the cells should be
>>        - First Cell: CIU clock phase shift value for tx mode.
>>        - Second Cell: CIU clock phase shift value for rx mode.
>> +      - Thrid Cell: Specifies the divider value for the card interface
>> +        unit (ciu) clock. This property is applicable only for Exynos5 SoC's and
>> +        ignored for Exynos4 SoC's. The valid range of divider value is 0 to 7.
>>
>>      Valid values for SDR and DDR CIU clock timing for Exynos5250:
>>        - valid value for tx phase shift and rx phase shift is 0 to 7.
>> @@ -79,8 +80,8 @@ Example:
>>                 broken-cd;
>>                 fifo-depth = <0x80>;
>>                 card-detect-delay = <200>;
>> -               samsung,dw-mshc-ciu-div = <3>;
>> -               samsung,dw-mshc-sdr-timing = <2 3>;
>> -               samsung,dw-mshc-ddr-timing = <1 2>;
>> +               samsung,dw-mshc-sdr-timing = <2 3 3>;
>> +               samsung,dw-mshc-ddr-timing = <1 2 3>;
>> +               samsung,dw-mshc-hs200-timing = <0 2 3>;
>
> You are breaking backward compatibility here.  If your change is
> merged then all old boards will instantly break.  Since the "dts" and
> code changes will likely be merged through different trees you'll end
> up with a bunch of broken trees until everything is merged together.
> Even if you don't subscribe to the stable bindings theory this is not
> acceptable.
>
yes the major concern in this series is probably this, which breaks
things unless everything merge in one go and via one tree. Thats why I
re-based everything including dts change on mmc-tree for this case and
added device-tree mailing list for more opinion etc.

> -Doug



-- 
Regards,
Alim