Hi
On 12/29/2016 09:53 AM, Kever Yang wrote:
> Hi Stefan,
>
> Thanks for your review comment.
> On 12/29/2016 02:35 AM, Stefan Herbrechtsmeier wrote:
>> Hi,
>>
>> Am 28.12.2016 um 12:01 schrieb Jaehoon Chung:
>>> On 12/28/2016 12:32 PM, Kever Yang wrote:
>>>> Init the clock rate to max-frequency from dts with clock driver api.
>>>>
>>>> Signed-off-by: Kever Yang <kever.y...@rock-chips.com>
>>> Reviewed-by: Jaehoon Chung <jh80.ch...@samsung.com>
>> This is an incorrect use of the max-frequency property.
>>
>> The max-frequency value limit the output clock of the mmc interface and
>> depends on the controller, circuit (level shifter), board and so on. It
>> doesn't represents the clock frequency of the controller.
>>
>> The clock setup inside the clock framework should use the
>> assigned-clock-rates property. The mmc driver should only enable the clock
>> and pass the clock rate together with the max-frequency to the mmc framework.
>
> I'm not good at mmc controller and driver framework, but seems that the sdhci
> core treats the max-frequency as the clock input from clock module, right?
> What if the mmc controller max-frequency is not equal to the clock module
> output which is possible? Does kernel deal with this, and how.
If my understanding is right, some controller should be broken the CLOCK_BASE
capability. (Refer to Linux kernel)
And then they needs to get value from CMU.
host->max_clk should be used the card's maximum value.
In Linux Kernel's case
if max_frequency property is defined, assigned to mmc->f_max
and host->f_max is assigned to clk_get_rate() value. (If Broken clock_base
capability)
And check "mmc->f_max > host->f_max" or "mmc->f_max == 0"
if true
then mmc->_f_max = f_max;
else
then mmc->f_max is used to "max_frequency" value.
In Conclusion,
host's maximum value is used. ("max_frequency" property is used to
QUIRK_BROKEN_CAP_CLOCK_BASE in Linux kernel.)
Kever's patch is not problem.
Best Regards,
Jaehoon Chung
>
> Thanks,
> - Kever
>>
>> Regards,
>> Stefan
>>
>>
>>
>>
>
>
>
>
>
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