Re: [PATCH V2 3/3] mmc: dw_mmc: Dont cut off vqmmc and vmmc

Doug Anderson
2014-08-27T04:14:11Z

Jaehoon,

On Tue, Aug 26, 2014 at 8:48 PM, Jaehoon Chung <jh80.chung@samsung.com> wrote:
> Hi, Doug,
>
> On 08/26/2014 12:25 AM, Doug Anderson wrote:
>> Jaehoon,
>>
>> On Mon, Aug 25, 2014 at 1:50 AM, Jaehoon Chung <jh80.chung@samsung.com> wrote:
>>> On 08/25/2014 05:13 PM, Ulf Hansson wrote:
>>>> On 22 August 2014 20:27, Sonny Rao <sonnyrao@chromium.org> wrote:
>>>>> On Fri, Aug 22, 2014 at 8:31 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>>>>>> On 22 August 2014 15:47, Yuvaraj Kumar C D <yuvaraj.cd@gmail.com> wrote:
>>>>>>> Exynos 5250 and 5420 based boards uses built-in CD# line for card
>>>>>>> detection.But unfortunately CD# line is on the same voltage rails
>>>>>>> as of I/O voltage rails. When we cut off vqmmc,the consequent card
>>>>>>> detection will break in these boards.
>>>
>>> I didn't know that use CD# line for card detect.
>>> And if CD# voltage rails and I/O voltage rail are same voltage, it doesn't make sense.
>>> Which card is used with same voltages? (eMMC? SD? SDIO?)
>>>
>>> Well, I have checked Exynos5250 and 5420, but it looks like not same rails.
>>
>> I'm not sure I totally understood what you said. In my manual I have
>> a table titled "Table 2-1 Exynos 5420 Pin List". Look in this table
>> for XMMC2CDN and XMMC2DATA_0. Look to the right of the table and
>> you'll see the power domain. For both it shows VDDQ_MMC2. If that
>> doesn't mean that the two are in the same voltage domain then I don't
>> know what does. Can you point to any examples where they have
>> different voltage domains?
> I think you're mis-understanding for it.
> Right, It's described at exynos5420, but it's not connected.

"It's not connected". What do you mean? If I were to guess I'd say
that on some particular board you're looking at they don't happen to
use the "CD" pin for card detect. If this is what you mean, it
doesn't help me. exynos5420-peach-pit does use the CD pin for card
detect. You can look at the DTS file and confirm it.

...or are you saying that the CD pin somehow changes voltage domains
when configured as a GPIO? I find that very hard to believe. What
voltage domain does it go to? If it goes to a 1.8V voltage domain
then that would be bad when vqmmc was 3.3V. If it goes to a 3.3V
voltage domain then that would be bad when vqmmc was 1.8V. Remember
that externally we've got a pull up to vqmmc.

Even if somehow magically we can read the card detect pin with vqmmc
off, we have an external pullup on this line that goes directly to the
"vqmmc" power rail. If the vqmmc power rail is off then this external
pull up would not work and would actually act as an external pull down
if you could somehow configure the internal line to be a pullup.

> Exynos4 series are also described, but we used the broken card detection scheme and power used one of "always-on" powers.
> Because Card-detection rail need to enable as "always-on".
>
> We don't need to consider this. I checked the circuit, this patch didn't need.
>
> exynos5 also used the gpio-pin for card-detection. And we can use the slot-gpio API.

When you say "exynos5", what do you mean here? Do you mean the smdk
for 5250, or something else?