linux-kernel - Re: [PATCH] mmc_spi: do propper retry managment in the block layer

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Message-ID: <20090530221613.GA642@console-pimps.org>
Date:	Sat, 30 May 2009 23:16:13 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Wolfgang Mües <wolfgang.mues@...rswald.de>
Cc:	Pierre Ossman <pierre@...man.eu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Mike Frysinger <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc_spi: do propper retry managment in the block layer
	- 3rd try

On Thu, May 28, 2009 at 11:52:26AM +0200, Wolfgang Mües wrote:
> 
> So somewhere I will need to have an error code filter based on the issued 
> command (class). Should this be in the driver(s)? Or should it be at the 
> location of the caller, in block.c?
> 

It should be in the function/file that makes the most sense.

> The advantages of putting it in block.c is that
> a) The command (class) is typically implicit given in the function, and no 
> need for a switch() statement.
> b) Only one handling for different drivers, not scattered through all(?) host 
> drivers.
> 

You know what, I was going to say that only block transaction stuff is
in block.c, but that's not true, there's loads of MMC protocol
knowledge in there too. I don't think there's a better place than
mmc/drivers/card/block.c, currently.

I would expect all this error handling and intimate knowledge of the
MMC/SD protocol to be in drivers/mmc/core, but that's not the
case. Which just seems strange to me.

> I must admit that I have difficulties to see a clear layering violation.
> There is no clear definition of which error codes should be reported to the 
> block layer. There is only a short list of codes with special meaning, but 
> not a full list of all used codes.
> 
> And some drivers are reporting codes like ENOMEM etc...
> 
> I see that Pierre wants to have a more smaller interface between drivers and 
> the upper layer, reporting only classes of errors, to have a more smaller and 
> cleaner code in the upper layer. But I think that this is a patch of its own, 
> and not in the context of the retry patch.
> 

I agree. That could be a separate patch.
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