[U-Boot] [PATCH v4 2/3] mmc: dw_mmc: Support bypass mode with the get_mmc_clk() method

[Jaehoon Chung]

Hi, 

On 08/07/2015 12:07 PM, Marek Vasut wrote:
> On Friday, August 07, 2015 at 05:00:24 AM, Simon Glass wrote:
>> Hi Marek,
> 
> Hi Simon,
> 
>> On 6 August 2015 at 20:58, Marek Vasut <marex at denx.de> wrote:
>>> On Friday, August 07, 2015 at 04:54:42 AM, Simon Glass wrote:
>>>> Hi Marek,
>>>
>>> Hi Simon,
>>>
>>>> On 6 August 2015 at 20:51, Marek Vasut <marex at denx.de> wrote:
>>>>> On Friday, August 07, 2015 at 04:16:28 AM, Simon Glass wrote:
>>>>>> Some SoCs want to adjust the input clock to the DWMMC block as a way
>>>>>> of controlling the MMC bus clock. Update the get_mmc_clk() method to
>>>>>> support this.
>>>>>>
>>>>>> Signed-off-by: Simon Glass <sjg at chromium.org>
>>>>>
>>>>> Hi Simon,
>>>>>
>>>>>> ---
>>>>>>
>>>>>> Changes in v4:
>>>>>> - Update commit message to indicate this patch is for the dw_mmc
>>>>>> driver
>>>>>>
>>>>>>  drivers/mmc/dw_mmc.c        |  2 +-
>>>>>>  drivers/mmc/exynos_dw_mmc.c |  2 +-
>>>>>>  include/dwmmc.h             | 16 +++++++++++++++-
>>>>>>  3 files changed, 17 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
>>>>>> index 8f28d7e..a034c3f 100644
>>>>>> --- a/drivers/mmc/dw_mmc.c
>>>>>> +++ b/drivers/mmc/dw_mmc.c
>>>>>> @@ -248,7 +248,7 @@ static int dwmci_setup_bus(struct dwmci_host
>>>>>> *host, u32 freq) * host->bus_hz should be set by user.
>>>>>>
>>>>>>        */
>>>>>>       
>>>>>>       if (host->get_mmc_clk)
>>>>>>
>>>>>> -             sclk = host->get_mmc_clk(host);
>>>>>> +             sclk = host->get_mmc_clk(host, freq);
>>>>>
>>>>> Why are you passing the @freq into get_mmc_clk() ? Shouldn't you call
>>>>> some clock framework function to determine the input frequency of the
>>>>> DWMMC block from within the get_mmc_clk() implementation instead ?
>>>>> What do you think please ?
>>>>
>>>> Well, yes. If such a clock frame work existed I would call it :-) We
>>>> do have a uclass now so we are getting there.
>>>
>>> Excellent, so do you really need this kind of patch ? :) Why don't you
>>> make just some kind of function -- get_dwmmc_clock() -- and call it
>>> instead ?
>>
>> This is sort-of what is happening. It is calling a function in the
>> host controller - i.e. the SoC's MMC controller. It is one step closer
>> to knowing the input clock to the dwmmc input clock. Note that it is
>> not the clock of the MMC bus itself, but the input clock to the dwmmc
>> logic block.
> 
> I don't think I quite understand wha,t you mean here. We're talking about
> obtaining the frequency of the clock which go into the DWMMC IP block,
> right ?
> 
> So, if you implement a function, say -- dwmmc_get_upstream_clock() -- and
> call it from within the implementation of the .get_mmc_clk(), which is
> specific for that particular chip of yours*, you don't need this patch.
> Or am I really missing something fundamental ?

Hmm. I don't know what purpose @freq is...just bypass?
@freq doesn't use wherever..I'm checking with u-boot-dm repository(mmc-working branch)
I wonder i'm also missing something like Marek.

Best Regards,
Jaehoon Chung

> 
> *the .get_mmc_clk() is specific to a chip, see for example exynos_dw_mmc.c
> 
> Best regards,
> Marek Vasut
>