linux-kernel - Re: [PATCH v3 10/13] mmc: mmci: add Qcom specifics of clk and datactrl registers.

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Message-ID: <5385AF47.8030909@linaro.org>
Date:	Wed, 28 May 2014 10:41:27 +0100
From:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:	Ulf Hansson <ulf.hansson@...aro.org>
CC:	Russell King <linux@....linux.org.uk>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Chris Ball <chris@...ntf.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm-msm@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v3 10/13] mmc: mmci: add Qcom specifics of clk and datactrl
 registers.

Hi Ulf,

On 26/05/14 22:38, Srinivas Kandagatla wrote:
>>>   2 files changed, 28 insertions(+)
>>>
>>> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
>>> index 17e7f6a..6434f5b1 100644
>>> --- a/drivers/mmc/host/mmci.c
>>> +++ b/drivers/mmc/host/mmci.c
>>> @@ -185,6 +185,10 @@ static struct variant_data variant_qcom = {
>>>          .fifosize               = 16 * 4,
>>>          .fifohalfsize           = 8 * 4,
>>>          .clkreg                 = MCI_CLK_ENABLE,
>>> +       .clkreg_enable          = MCI_QCOM_CLK_FLOWENA |
>>> +                                 MCI_QCOM_CLK_FEEDBACK_CLK,
>>
>> Obviously I don't have the in-depth knowledge about the Qcom variant,
>> but comparing the ST variant here made me think.
>>
>> Using the feeback clock internal logic in the ST variant, requires the
>> corresponding feedback clock pin signal on the board, to be
>> routed/connected. Typically we used this for SD cards, which involved
>> using an external level shifter circuit.
>>
>> Is it correct to enable this bit for all cases, including eMMC?
>>
> You are correct, FBCLK should specific to the board, and I will try to
> do something on the same lines as ST variant in next version.
I get lot of I/O errors when I remove this flag for test.

I rechecked schematics and datasheet, the feedback clk that we refer 
here is the the feedback clk from CLK pad, there is no separate input 
pad for fbclk. So I think this is internally feedbacked clk.

This selection is configuring bits to latch data and command coming in 
using feedback clock from CLK pad.

I will make sure that the macro is named more appropriately to reflect 
the same.

thanks,
srini
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