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

[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:

diff --git a/drivers/mmc/host/mxs-mmc.c b/drivers/mmc/host/mxs-mmc.c
index 206fe49..2a3b9c9 100644
--- a/drivers/mmc/host/mxs-mmc.c
+++ b/drivers/mmc/host/mxs-mmc.c
@@ -679,15 +682,20 @@ static int mxs_mmc_probe(struct platform_device *pdev)
        /* set mmc core parameters */
        mmc->ops = &mxs_mmc_ops;
        mmc->caps = MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED |
-                   MMC_CAP_SDIO_IRQ | MMC_CAP_NEEDS_POLL;
+                   MMC_CAP_SDIO_IRQ;

        of_property_read_u32(np, "bus-width", &bus_width);
        if (bus_width == 4)
                mmc->caps |= MMC_CAP_4_BIT_DATA;
        else if (bus_width == 8)
                mmc->caps |= MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA;
-       host->wp_gpio = of_get_named_gpio_flags(np, "wp-gpios", 0, &flags);

+       if (of_find_property(np, "non-removable", NULL))
+               mmc->caps |= MMC_CAP_NONREMOVABLE;
+       else
+               mmc->caps |= MMC_CAP_NEEDS_POLL;
+
+       host->wp_gpio = of_get_named_gpio_flags(np, "wp-gpios", 0, &flags);
        if (flags & OF_GPIO_ACTIVE_LOW)
                host->wp_inverted = 1;


In theory, and according to the mmc bindings doc, this flag must assume the card is 
always present. However the MMC core function mmc_rescan() will still call at least 
once the get_cd() hook, which in the mxs-mmc.c returns the value of the CD line. In my 
platform (where the CD line is not connected) this is returning 0, so I needed to do 
the following:

diff --git a/drivers/mmc/host/mxs-mmc.c b/drivers/mmc/host/mxs-mmc.c
index 206fe49..2a3b9c9 100644
--- a/drivers/mmc/host/mxs-mmc.c
+++ b/drivers/mmc/host/mxs-mmc.c
@@ -95,6 +95,9 @@ static int mxs_mmc_get_cd(struct mmc_host *mmc)
        struct mxs_mmc_host *host = mmc_priv(mmc);
        struct mxs_ssp *ssp = &host->ssp;

+       if (mmc->caps & MMC_CAP_NONREMOVABLE)
+               return 1;
+
        return !(readl(ssp->base + HW_SSP_STATUS(ssp)) &
                 BM_SSP_STATUS_CARD_DETECT);
 }

to return a 1 when the driver should assume that the card is there. I wonder however 
if this should be a global mmc patch instead, and have mmc_rescan() not call the host 
get_cd() hook at all if MMC_CAP_NONREMOVABLE is set.

Regards,
--
Héctor Palacios
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