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Date: Thu, 6 Jul 2006 15:22:03 -0700
From: Andrew Morton <akpm@osdl.org>
To: linas@austin.ibm.com (Linas Vepstas)
Cc: greg@kroah.com, linux-pci@atrey.karlin.mff.cuni.cz,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Fix PCI error token awkward value
Message-Id: <20060706152203.5721d54e.akpm@osdl.org>
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linas@austin.ibm.com (Linas Vepstas) wrote:
>
> 
> 
> The pci channel state token currently has a poor choice of values;
> there  are two ways of indicating that "everything's OK": 0 and 1.
> This is a bit of a burden.
> 
> If a devce driver wants to check if the pci channel is in a working
> or a disconnected state, the driver writer must perform checks similar
> to
> 
>    if((pdev->error_state != 0) &&
>       (pdev->error_state != pci_channel_io_normal)) {
>          whatever();
>    }
> 
> which is rather akward. The first check is needed because 
> stuct pci_dev is inited to all-zeros. The scond is needed 
> because the error recovery will set the state to 
> pci_channel_io_normal (which is not zero).
> 
> This patch fixes this awkwardness.
> 

eww.

> 
> Index: linux-2.6.17-mm3/include/linux/pci.h
> ===================================================================
> --- linux-2.6.17-mm3.orig/include/linux/pci.h	2006-06-27 11:39:16.000000000 -0500
> +++ linux-2.6.17-mm3/include/linux/pci.h	2006-07-06 15:15:09.000000000 -0500
> @@ -85,7 +85,7 @@ typedef unsigned int __bitwise pci_chann
>  
>  enum pci_channel_state {
>  	/* I/O channel is in normal state */
> -	pci_channel_io_normal = (__force pci_channel_state_t) 1,
> +	pci_channel_io_normal = (__force pci_channel_state_t) 0,
>  
>  	/* I/O to channel is blocked */
>  	pci_channel_io_frozen = (__force pci_channel_state_t) 2,

It needs a comment to prevent people from breaking it in the future, and
to help people who are trying to work out why the heck the kernel is
looking for a particular state in something which hasn't been set to that
state.

Also, it's a bit odd that we've gone and left a hole in the enum space.


Wouldn't it be better to sort out our initialisation so we don't actually
need this memset-equals-pci_channel_io_normal trick?  pci_scan_device()
looks like a good place..