Re: [PATCH RFC] ARM: dts: mxs: leave card detect out of common mmcpins config

[Hector Palacios]

On 04/09/2013 12:51 PM, Marek Vasut wrote:
> Hi Hector,
>
> > Dear Marek Vasut,
> >
> > On 04/09/2013 10:15 AM, Marek Vasut wrote:
> > > Dear Hector Palacios,
> > >
> > > > Dear Marek Vasut,
> > > >
> > > > On 04/08/2013 06:28 PM, Marek Vasut wrote:
> > > > > Dear Shawn Guo,
> > > > >
> > > > > > On Mon, Apr 08, 2013 at 03:58:05PM +0200, Hector Palacios wrote:
> > > > > > > On 04/08/2013 02:48 PM, Shawn Guo wrote:
> > > > > > > > On Mon, Apr 08, 2013 at 12:12:20PM +0200, Hector Palacios wrote:
> > > > > > > > > MicroSD card sockets don't usually have card detect line. This pin
> > > > > > > > > is actually not needed for the MMC to work and it is more of a
> > > > > > > > > platform design decission to have it.
> > > > > > > > > The card detect pin already has a configuration entry of its own:
> > > > > > > > > 'mmc0_cd_cfg' so we complete the iomux configuration here and let
> > > > > > > > > platforms to include it or not depending on whether the card detect
> > > > > > > > > line is routed to the SD socket.
> > > > > > > >
> > > > > > > > Sounds sensible.
> > > > > > > >
> > > > > > > > > Signed-off-by: Hector Palacios <hector.palacios@xxxxxxxx>
> > > > > > > > > ---
> > > > > > > > >
> > > > > > > > > Hello,
> > > > > > > > >
> > > > > > > > > All imx28 based platforms except 'bluegiga,apx4devkit' and
> > > > > > > > > 'schulercontrol,imx28-sps1', use 'mmc0_cd_cfg' in their mmc
> > > > > > > > > configuration so please check whether this patch would break these
> > > > > > > > > platforms.
> > > > > > > >
> > > > > > > > I just tested the patch on imx28-evk and card-detection still works.
> > > > > > > > So patches applied, thanks.
> > > > > > >
> > > > > > > The EVK and most platforms will work because they are using
> > > > > > > 'mmc0_cd_cfg' so actually this patch does not change anything on
> > > > > > > them.
> > > > > > > Platforms 'bluegiga,apx4devkit' and 'schulercontrol,imx28-sps1'
> > > > > > > however are not referencing 'mmc0_cd_cfg' so after applying this
> > > > > > > patch they will have unconfigured CD line and they may break.
> > > > > >
> > > > > > Ah, yes.  I thought that any board that has CD support has to
> > > > > > reference 'mmc0_cd_cfg'.  That's not necessarily true.
> > > > > >
> > > > > > > The driver will call get_cd() upon probing, which returns the status
> > > > > > > of the CD line. Please check these two platforms before applying.
> > > > > >
> > > > > > Ok, let's wait for people owning the boards to confirm.
> > > > >
> > > > > Maybe you want to use MMC_CAP_NEEDS_POLL as was noted by someone before
> > > > > on the olinuxino -- the slot is there, it's just the CD line that's
> > > > > missing.
> > > >
> > > > I'm not sure of what you mean. The mxs-mmc.c driver already sets the
> > > > MMC_CAP_NEEDS_POLL flag by default in the probe() function. My platform
> > > > does not even route the CD line because the microSD socket does not have
> > > > it.
> > > > So what I have done is modify the driver to parse the property
> > > > 'non-removable' from the device tree in order to set the
> > >
> > > > MMC_CAP_NONREMOVABLE flag:
> > > Yes, I get it. I have two remarks still:
> > > 1) The card is removable (you can pull it out from olinuxino's slot)
> >
> > True, I misunderstood the use of 'non-removable'. So I guess I could use
> > 'broken-cd' property instead, right?
>
> Yep, seems ok.
>
> > > 2) Why is the NEEDS_POLL set by default ?
> >
> > Because the CD line cannot cause an interrupt in this controller.
>
> Ok, understood.
>
> NOTE: Here is an idea -- we can solve this the same way it's solved with the MXC
> SDHCI, configure the CD pin(s) as GPIO(s) and then they'll be able to generate
> interrupt. On the other hand, this shall definitelly be done in a separate
> patch.
>
> > > 3) Does the NEEDS_POLL not solve the issue with missing CD line?
> >
> > No. CD polling relies on the status register. The field CARD_DETECT in
> > HW_SSP_STATUS register directly reflects the state of the SSP_DETECT input
> > pin. If the pin is not connected it can have any value, so I guess we need
> > a custom flag on the driver:

Patch available in this other thread (pending resubmission):
http://comments.gmane.org/gmane.linux.kernel.mmc/19982

With this, card detection works via polling even if you don't use the Card Detect line.

Regards,
--
Héctor Palacios
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