Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc

From: Doug Anderson <dianders@chromium.org>
To: Addy <addy.ke@rock-chips.com>
Cc: "Ulf Hansson" <ulf.hansson@linaro.org>,
	"Rob Herring" <robh+dt@kernel.org>,
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Subject: Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc
Date: Mon, 24 Nov 2014 21:36:04 -0800	[thread overview]
Message-ID: <CAD=FV=U9Hh-OR2aGh6Q9YAwnP8AuAbQtogD=7wQxgg9XvoWTMw@mail.gmail.com> (raw)
In-Reply-To: <5473EB8B.3000803@rock-chips.com>

Addy,

On Mon, Nov 24, 2014 at 6:38 PM, Addy <addy.ke@rock-chips.com> wrote:
>> In worst case scenario, VDD = 3.6V and VIO = 2.7V. That gives as the
>> factor of 0.75, thus we are inside spec but without margins.
>
> * From eMMC4.5 spec:
>   1. (VDDF)vcc: Supply voltage for flash memory,  which is  2.7v -- 3.3v
>   2. (VDD)vccq: Supply voltage for memory controller, which is  1.7v --
> 1.95v  and 2,7v -- 3.6v
>
> * And from RK3288 datasheet:
>   Digtial GPIO Power(SDMMC0_VDD --> vccq) is 3.0v -- 3.6v and 1.62v - 1.98v
>
> So I think:
> 3.3v:  (2.7v < vccq < 3.6v)   &&  (3.0v < vccq < 3.6v)  ==> (3.0v < vccq <
> 3.6v)
> 1.8v:  (1.7v < vccq < 1.95v)  && (1.62v < vccq < 1.98v) ==> (1.7v < vccq <
> 1.95v)
>
> and (2.7v < vcc < 3.3v)
>
> * And according to our hardware engineer:
>   All of supply voltage must have +/- 10% cushion.
>
> * And we have found in some worse card that there is 200mv voltage collapse
> when these card is insert.
>
> So I think the best resolution is that vcc and vccq is configurable int dt
> table.

Ah, interesting.  ...so what we really need to be able to do is to say
that the regulator we for vqmmc have supports the ranges 3.0V - 3.3V
and 1.7V - 1.95V but not anything in between 1.95V ad 3.0V.  I have no
idea how to express that in the regulator framework.

Technically you could take the IO Voltage Domains code (responsible
for choosing the 1.8V range or the 3.3V range) and have it communicate
the requirements to the regulator framework if you could figure out
how to communicate them.

...of course if you implemented my suggestion of keeping vqmmc as the
highest voltage <= vmmc then maybe the whole point is moot and we
don't have to figure it out.  Just make sure that vmmc never goes
below 3.0V.

-Doug