Re: [PATCH 1/4] mmc: core: add support for hardware reset gpio line

[Sjoerd Simons <sjoerd.simons@collabora.co.uk>]

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On Fri, 2015-01-30 at 11:37 +0100, Marek Szyprowski wrote:
> Hello,
> 
> On 2015-01-29 11:56, Javier Martinez Canillas wrote:
> > On Thu, Jan 29, 2015 at 10:15 AM, Marek Szyprowski
> > <m.szyprowski@samsung.com> wrote:
> >>> Also, I wonder whether we could extend the mmc-pwrseq to cover your
> >>> case? Did you consider that as an option?
> >>
> >> I didn't consider mmc-pwrseq yet. For me it looked straightforward to
> > I agree with Ulf that using mmc-pwrseq would be a good solution and in
> > fact I think the pwrseq_simple [0] driver will fit your use case since
> > it supports a reset GPIO pin which is what many WLAN chips attached to
> > a SDIO interface use.
> 
> Ok, I've checked mmc-prwseq and mmc-pwrseq-simple. I also checked the
> hardware and it mmc-pwrseq-simple cannot be used directly.
> 
> Although the signal is called RSTN (on Odroid U3 schema), the eMMC card
> gets resetted not on low line level, but during the rising edge. This RSTN
> line is also pulled up by the external resistor. However, the strangest
> thing is the fact that the default SoC configuration (which is applied
> during hw reset) for this GPIO line is input, pulled-down. The SoC
> internal pull-down is stronger than the external pull up, so in the end,
> during the SoC reboot the RSTN signal is set to zero. Later bootloader
> disables the internal pull-down.
> 
> To sum up - to perform proper reboot on Odroid U3/XU3, one need to set
> RSTN to zero, wait a while and the set it back to 1.

> To achieve this with mmc-pwrseq-simple, I would need to modify the power_off
> callback to toggle reset line to zero and back to one. This however might
> not be desired to other sd/mmc cards used with mmc-pwrseq-simple.
> 
> I can also provide separate mmc-pwrsrq-odroid driver, which will be very
> similar to mmc-pwrseq-simple.

Apart from the initial odd setup of the SoC pins this is the standard
H/W reset operation specified by Jedec 4.4:

* pull the reset line down for at least 1us
* pull the line up again
* Wait at least 200us before sending commands

(sdhci_pci_int_hw_reset also implements this).

I'm not sure what the determining factor is for a pwrseq driver vs. it
being part of the mmc core would be. But if you do a pwrseq driver it
shouldn't be board specific e.g. call it mmc-pwrseq-emmc4.4 instead of
-odroid?


-- 
Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Collabora Ltd.

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