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

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Date:	Thu, 16 Oct 2014 09:10:37 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Alim Akhtar <alim.akhtar@...il.com>
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

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?


> 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.


> 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.


-Doug
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