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

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Date:	Tue, 9 Apr 2013 11:00:09 +0200
From:	Hector Palacios <hector.palacios@...i.com>
To:	Marek Vasut <marex@...x.de>
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

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?

> 2) Why is the NEEDS_POLL set by default ?

Because the CD line cannot cause an interrupt in this controller.

> 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:

diff --git a/drivers/mmc/host/mxs-mmc.c b/drivers/mmc/host/mxs-mmc.c
index 206fe49..ec0874b 100644
--- a/drivers/mmc/host/mxs-mmc.c
+++ b/drivers/mmc/host/mxs-mmc.c
@@ -72,6 +72,7 @@ struct mxs_mmc_host {
         int                             sdio_irq_en;
         int                             wp_gpio;
         bool                            wp_inverted;
+       bool                            cd_broken;
  };

  static int mxs_mmc_get_ro(struct mmc_host *mmc)
@@ -95,6 +96,9 @@ 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 (host->cd_broken)
+               return 1;
+
         return !(readl(ssp->base + HW_SSP_STATUS(ssp)) &
                  BM_SSP_STATUS_CARD_DETECT);
  }
@@ -686,8 +690,11 @@ static int mxs_mmc_probe(struct platform_device *pdev)
                 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, "broken-cd", NULL))
+               host->cd_broken = 1;
+
+       host->wp_gpio = of_get_named_gpio_flags(np, "wp-gpios", 0, &flags);
         if (flags & OF_GPIO_ACTIVE_LOW)
                 host->wp_inverted = 1;

Thank you for your comments.
-- 
Héctor Palacios
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