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

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Message-id: <54448023.1050008@samsung.com>
Date:	Mon, 20 Oct 2014 12:23:15 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Alim Akhtar <alim.akhtar@...il.com>,
	Doug Anderson <dianders@...omium.org>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Seungwon Jeon <tgih.jun@...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.

On 10/17/2014 09:44 PM, Alim Akhtar wrote:
> 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.

I know there is no other requirement for detecting card. 
So this patch can be applied after testing the above case(suspend/resume).

Best Regards,
Jaehoon Chung

>>
> 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
> 
> 
> 

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