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

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Date:	Thu, 23 Oct 2014 10:13:10 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Alim Akhtar <alim.akhtar@...il.com>,
	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>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Subject: Re: [PATCH] mmc: dw_mmc: Remove old card detect infrastructure

Dear, Doug.

On 10/23/2014 01:36 AM, Doug Anderson wrote:
> Hi,
> 
> On Sun, Oct 19, 2014 at 8:23 PM, Jaehoon Chung <jh80.chung@...sung.com> wrote:
>> 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).
> 
> I put a kernel based upon 3.17 on an exynos5250-snow (specifically
> git://git.collabora.co.uk/git/user/javier/linux.git branch
> max77802-op-modes-v3, git hash 98cf5a0).  Snow uses the builtin card
> detect on dw_mmc.  Resume wasn't terribly reliable to start with even
> without my patch (it often woke up right after suspend), but it worked
> well enough for testing.  I tested the following scenarios:
> 
> 1. Leave card in and mounted.  Suspend/resume.  Card is still usable
> after resume
> 
> 2. Suspend and insert card.  Resume.  Card is detected upon resume.
> 
> 3. Suspend and remove card.  Resume.  Card is removed upon resume.
> 
> How does that sound?

I think these test cases are enough, and if it's working fine, sounds good.

Acked-by: Jaehoon Chung <jh80.chung@...sung.com>

Best Regards,
Jaehoon Chung

> 
> -Doug
> 

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