Re: [PATCH 3/3] ARM: dts: exynos5422-odroidxu3: Added UHS-I bus speed support

[Doug Anderson]

Hi,

On Tue, Oct 13, 2015 at 6:06 PM, Alim Akhtar <alim.akhtar@xxxxxxxxx> wrote:
> +Doug
> Hello,
> AFAIR, dw_mmc host controller does support UHS-I [1], specially SDR50
> and SDR104 modes.
>
> [1]: http://www.spinics.net/lists/linux-mmc/msg28186.html
>
> What I remember is, one need to set "broken-cd" property also in order
> to make it work because of the vqmmc and vmmc connection on board. I
> didn't find the link right now, but you can search on the web, there
> was a long discussion about handling this.
> Have not checked it recently, so not sure if this got broken somehow.

Right.  It _shouldn't_ be possible to add "vmmc/vqmmc" supplies to
your DTS (which you do in patch 2/3) and also to use the "gpc2-2" pin
for card detect (even if you configure it as a GPIO).  Once you add
"vmmc/vqmmc" then Linux ought to be turning these regulators off when
no card is plugged in.  Presumably the "vqmmc" regulator is hooked up
to the "VDDQ_MMC2".  If you look in the user manual for 5422 you can
see that "GPC2[2]/SD_2_CDn" has power domain "VDDQ_MMC2".  Thus you
really shouldn't be using that pin when vqmmc is off.  I think at some
point someone claimed that it still worked for them, but nobody could
ever explain why.  Full discussion at
<https://patchwork.kernel.org/patch/4763881/>

---

In case it matters, comments on stuff from earlier in the thread:

* As people pointed out, exynos5422 certainly supports all these modes
(including DDR50) in the SoC.

* Just because the SoC supports these modes doesn't mean that the
boards do, which is why the SoC .dtsi doesn't include them.  Thus,
this patch is "right" in that it changes a board-specific file.

* As Krzysztof points out this board doesn't "add" support but rather
"enables" support.  The distinction is subtle.

* You might be able to get DDR50 working, but probably better to just
start with SDR modes.  Previously I never attempted to get DDR50 cards
working, so possibly the software needs extra work?


-Doug
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