linux-kernel - Re: [PATCH] mmc: change mmc_gpio_get

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Date:	Mon, 19 Aug 2013 16:36:00 -0700
From:	"Christian Daudt" <csd@...adcom.com>
To:	"Guennadi Liakhovetski" <g.liakhovetski@....de>
cc:	"Chris Ball" <cjb@...top.org>, "Shawn Guo" <shawn.guo@...aro.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	"arm@...nel.org" <arm@...nel.org>
Subject: Re: [PATCH] mmc: change mmc_gpio_get_cd to call non-sleep gpio

On 13-08-08 02:10 PM, Christian Daudt wrote:
> On 13-08-08 02:06 PM, Guennadi Liakhovetski wrote:
>> On Thu, 8 Aug 2013, Christian Daudt wrote:
>>
>>> Given that mmc_gpio_get_cd can be called in softirq
>>> context (by sdhci_tasklet_card -> sdhci_card_event ->
>>> sdhci_do_get_cd -> mmc_gpio_get_cd ), it is necessary
>>> for it to use gpio_get_value instead of
>>> gpio_get_value_cansleep
>>> Note that at present sdhci_card_event gets called both
>>> from mmc_gpio_cd_irqt and sdhci_tasklet_card, and from
>>> both it gets called immediately while the actual cd
>>> processing is debounced to 200ms later. I think that
>>> the better solution might be to move the sdhci_card_event
>>> callback into mmc_rescan and remove it from its 2
>>> present locations. That way the cd related callbacks
>>> are aligned with the actual cd detection code. I can
>>> submit a follow-up patch with these mods if that sounds
>>> like a better way to solve this.
>>>
>>> Signed-off-by: Christian Daudt <csd@...adcom.com>
>> I don't think this is a right approach. It will Oops if the card-detect
>> GPIO is provided by, e.g. an I2C GPIO controller. Instead the driver
>> should be fixed to only call this function from a sleeping context.
> I don't think that card-detect would ever be tied to i2c but I might 
> be wrong on that one... If there's agreement that moving 
> sdhci_card_event into just being called from mmc_rescan is the better 
> way to solve this, then I'll drop this patch and replace it with one 
> that does just that.
>
>  Thanks,
>    csd
>
[adding arm@...nel.org for more input]
Guennadi,
  While I can't see card-detect coming in through i2c gpio controller, I 
think that moving this out of the sleeping context (and into mmc_rescan) 
is probably the better solution anyways. So I'll drop this patch and 
send another one with that change instead.


  Thanks,
    csd


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