linux-kernel - Re: [PATCH] mmc: dw_mmc: Remove old card detect infrastructure

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Message-ID: <CAGOxZ51x8cd9XmNg49aaUdZQkw-hhEA-mC=34ZSjLf0XF8Zbvw@mail.gmail.com>
Date:	Fri, 17 Oct 2014 18:14:45 +0530
From:	Alim Akhtar <alim.akhtar@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Addy Ke <addy.ke@...k-chips.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Andrew Bresticker <abrestic@...omium.org>,
	Chris Ball <chris@...ntf.net>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: dw_mmc: Remove old card detect infrastructure

Hi Doug,

On Thu, Oct 16, 2014 at 9:40 PM, Doug Anderson <dianders@...omium.org> wrote:
> Alim,
>
> On Thu, Oct 16, 2014 at 5:57 AM, Alim Akhtar <alim.akhtar@...il.com> wrote:
>> Hi Doug,
>>
>> On Tue, Oct 14, 2014 at 10:03 PM, Doug Anderson <dianders@...omium.org> wrote:
>>> The dw_mmc driver had a bunch of code that ran whenever a card was
>>> ejected and inserted.  However, this code was old and crufty and
>>> should be removed.  Some evidence that it's really not needed:
>>>
>>> 1. Is is supposed to be legal to use 'cd-gpio' on dw_mmc instead of
>>>    using the built-in card detect mechanism.  The 'cd-gpio' code
>>>    doesn't run any of the crufty old code but yet still works.
>>>
>>> 2. While looking at this, I realized that my old change (369ac86 mmc:
>>>    dw_mmc: don't queue up a card detect at slot startup) actually
>>>    castrated the old code a little bit already and nobody noticed.
>>>    Specifically "last_detect_state" was left as 0 at bootup.  That
>>>    means that on the first card removal none of the crufty code ran.
>>>
>> Yes, right most of these codes are _almost_ never call. But I see
>> dw_mci_reset() being called on card removal (after first
>> insert/removal).
>
> Right.  The old crufty code was called on the 2nd removal, not the
> 1st.  That meant that the two were accidentally different.  My point
> was that if the old code was really required that someone would have
> noticed crashes on the 1st removal after each boot.  Since nobody is
> reporting crashes with that then it means it can't be too terrible.
>
> One thing to note: I remember in the last Chromebook project you were
> trying to track down crashes associated with constant eject / insert
> of SD Cards.  I wonder if my patch will fix these crashes?
>
Ah, yes, reproducing that and checking with this patch will be really
interesting.

>
>> I tested this on exynos5800 and this looks working fine. We need to
>> test once cross suspend/resume as well.
>
> Good idea.  Can you test that?  I know that there's been lots of flux
> with suspend/resume on exynos and I'm not sure I have all the latest
> patches, but I'll search for them if you are unable to test easily.
>
Sure, I will do that..but probably sometime next week, as I will out
of office for few days.
>
>> And as Jaehoon pointed out,probably lets look in TRM if there are some
>> recommended  steps for cd-detect.
>> Otherwise this looks good to me.
>
> If you see some other requirement than the one I addressed in my email
> to Jaehoon, please let me know.
>
Well, as most of the current CD detect code are dead code, so lets see
more test results, specially across a suspend/resume and warm reboot
test and take this forward.
>
> -Doug



-- 
Regards,
Alim
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