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

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Date:	Wed, 22 Oct 2014 09:36:58 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Jaehoon Chung <jh80.chung@...sung.com>
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

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?

-Doug
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