linux-kernel - Re: [PATCH] mmc : Use wait_for_completion_timeout() instead of wait_for

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Date:	Tue, 20 Sep 2011 09:39:43 +0200
From:	Ulf Hansson <ulf.hansson@...ricsson.com>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	"cjb@...top.org" <cjb@...top.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc : Use wait_for_completion_timeout() instead of wait_for_completion
 in case of write.

Namjae Jeon wrote:
> host controller can not rise timeout interrupt in write not read in DMA status. 
> because host can just know whether card is finish to program to use busy line. 
> If unstable card is keep holding busy line while writing using DMA.
> hang problem happen by wait_for_completion. so I think that mmc driver need some exception to avoid this problem.
> I suggest to use wait_for_completion_timeout instead of wait_for_completion.
> 

I see what you are trying to solve, but you can never calculate the 
timeout for this type of operation in such a way. Your timeout involves 
the entire data write operation, how can you ever know how long this 
will take?

I think a much better approach is to make you host driver not using 
"busy signaling" (if that is possible), thus when the DMA job is done 
call mmc_request_done to finalize the data transfer. The mmc framework 
will then send a CMD13 (SEND_STATUS) to make sure the data is written 
before issuing the next request.

BR
Ulf Hansson
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