linux-kernel - Re: [PATCH RFC] ARM: dts: mxs: leave card detect out of common mmc pins config

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Message-Id: <201304091251.59359.marex@denx.de>
Date:	Tue, 9 Apr 2013 12:51:59 +0200
From:	Marek Vasut <marex@...x.de>
To:	Hector Palacios <hector.palacios@...i.com>
Cc:	Shawn Guo <shawn.guo@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"maxime.ripard@...e-electrons.com" <maxime.ripard@...e-electrons.com>,
	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH RFC] ARM: dts: mxs: leave card detect out of common mmc pins config

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@...i.com>
> >>>>>>> ---
> >>>>>>> 
> >>>>>>> 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:

Understood!

Best regards,
Marek Vasut
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