linux-kernel - Re: [PATCH 3/3] mmc: host: omap_hsmmc: Add custom card detect irq handler

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Date:	Wed, 22 Jul 2015 13:01:21 +0530
From:	Vignesh R <vigneshr@...com>
To:	Andreas Fenkart <afenkart@...il.com>
CC:	Ulf Hansson <ulf.hansson@...aro.org>,
	Tony Lindgren <tony@...mide.com>, NeilBrown <neilb@...e.de>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mmc: host: omap_hsmmc: Add custom card detect irq
 handler

Hi Andreas,

On 07/21/2015 01:46 PM, Andreas Fenkart wrote:
> Hi Vignesh,
> 
> Generally I don't like this patch, it will make it harder, not easier,
> to maintain the omap hsmmc driver. Also given that the bug occurs
> rarely, people will be reluctant to clean it up later or accept
> patches.
> 
> see also comments below
> 
[snip]
> 2015-06-22 15:18 GMT+02:00 Vignesh R <vigneshr@...com>:
>>
> 
>> But calls to omap_hsmmc_card_init or omap_hsmmc_get_cd are in the same
>> mmc_rescan thread. Hence, moving the recovery code to init_card does not
>> help.
> 
> what about clearing any pending transfer in
> - mmc_gpio_cd_irqt, or
> - mmc_detect_change
> 
> e.g. trigger the later mentioned .card_event callback from those
> functions, instead mmc_rescan? Then you can install your
> omap_hsmmc_request_clear as the card_event callback. This makes your
> custom isr handler redundant, actually your isr handler became
> standard.
> 

I looked  at the commit fa372a51cb5f93800f711473e5a36e0e0c9a8f00 which
moved .card_event out of mmc_gpio_cd_irqt. It points to two threads
where discussion to move .card_event to mmc_rescan happened[1][2]. The
concern there was this callback was being called from "atomic context"
but, I don't understand how threaded irq is "atomic context". (I am not
sure, if this is because those drivers have irqs disabled till threaded
irq is complete) But, I believe moving card_event callback back to
mmc_gpio_cd_irqt may break some drivers.
I will look into this further.
Do you have any insight on this commit? Thanks!

[1]https://lkml.org/lkml/2014/3/19/79
[2]https://lkml.org/lkml/2013/8/19/539

-- 
Regards
Vignesh
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