linux-kernel - Re: [PATCH 1/3] mmc: dw_mmc: Increase cmd11 timeout to 500ms

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Message-id: <55233A24.1000803@samsung.com>
Date:	Tue, 07 Apr 2015 11:00:04 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Doug Anderson <dianders@...omium.org>,
	Jaehoon Chung <jh80.chung@...sung.com>
Cc:	Seungwon Jeon <tgih.jun@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Addy Ke <addy.ke@...k-chips.com>,
	Alexandru Stan <amstan@...omium.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mmc: dw_mmc: Increase cmd11 timeout to 500ms

Hi, Doug.

On 04/07/2015 04:32 AM, Doug Anderson wrote:
> Jaehoon,
> 
> On Mon, Apr 6, 2015 at 3:46 AM, Jaehoon Chung <jh80.chung@...sung.com> wrote:
>> Hi, Doug.
>>
>> On 04/04/2015 03:13 AM, Doug Anderson wrote:
>>> The Designware databook claims that cmd11 should be finished in 2ms,
>>> but my testing showed that not to be the case in some situations.
>>> I've seen cmd11 timeouts of up to 130ms (!) during reboot tests.
>>> Let's bump the timeout way up so that we're absolutely sure.  CMD11 is
>>> only sent during card insertion, so this extra timeout shouldn't be
>>> terrible.
>>
>> Is it h/w problem? Could you explain to me about "some situations"?
>> As you said, this timeout only used during card inserting. So, it's not critical..
>> But there is much different between 2ms and 500ms(or 130ms).
> 
> Very good question, and it makes sense to dig into this...
> 
> OK, I think I've got it.  Dang printk bites me again.  I have serial
> console enabled and my printouts were actually causing these delays.
> With serial console turned off I reliably get ~280us for the interrupt
> to fire (tested across SD and WiFi across 137 + 128 + 111 + 127 = 503
> reboots)

Oh..agreed. I also think printouts can be caused the delay.
Thanks for your explanation.

> 
> I think it makes sense to land this patch anyway, but with an updated
> description.  I'm happy to repost this or happy if you just want to
> update the description when applying.

To save your time, when applying, i will do the updating description.

Best Regards,
Jaehoon Chung

> 
> ---
> 
> Although the cmd11 interrupt should come within 2ms, that's a very
> short time.  Let's increase the timeout to be really sure that we
> don't get an accidnetal timeout.  One case in particular this is
> useful is if you've got a serial console and printk in just the right
> places.  Under that scenario I've seen delays of up to 130ms before
> the interrupt fired.
> 
> CMD11 is only sent during card insertion, so this extra timeout
> shouldn't be terrible.
> 
> ---
> 
> -Doug
> --
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