linux-kernel - Re: [RFC][PATCH][TRIVIAL] System ACE fails in look for root devices

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Date:	Thu, 13 Oct 2011 11:29:58 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Petr Cvek <petr.cvek@....cz>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH][TRIVIAL] System ACE fails in look for root devices

On Thu, Oct 13, 2011 at 01:02:42PM +0200, Petr Cvek wrote:
> Hello,
> 
> I sent this mail some time ago, but nobody replied :-(.
> 
> 
> I'm using microblaze linux on ML506 board and I found problem with
> SystemACE CF driver.
> 
> When xsysace driver is probed, and dts file does not include entry
> "port-number" (existence of line not actually tested) on line:
> 
> 	of_property_read_u32(dev->dev.of_node, "port-number", &id);
> 
> kernel fails to boot with this message:
> 
> 	<4>VFS: Cannot open root device "xsa2" or unknown-block(0,0)
> 	<4>Please append a correct "root=" boot option; here are the
> available partitions:
> 	<4>fff:ffff0     990864 xs`  (driver?)
> 	<4>  fff:ffff1     124960 xs`1 00000000-0000-0000-0000-000000000000
> 	<4>  fff:ffff2     865872 xs`2 00000000-0000-0000-0000-000000000000
> 	<0>Kernel panic - not syncing: VFS: Unable to mount root fs on
> unknown-block(0,0)
> 
> (note xs` xs`1 xs`2 partition names)
> 
> So I've done some searching and found "ace->id" variable, which has
> value "-1". Because this value define letter of drive and is
> incremented by 'a', then with its value of -1, creates letter before
> 'a' thus '`'.
> 
> "ace->id" value is assigned in ace_probe function on line
> 
>       of_property_read_u32(dev->dev.of_node, "port-number", &id);
>       if (id < 0)
>           id = 0;

However, of_property_read_u32() can only accept a u32 value, not an
int, so this needs to be solved with two variables to be correct:

	int id;
	u32 tmp;
	id = dev->id;
	if (of_property_read_u32(dev->dev.of_node, "port-number", &tmp)
		id = tmp;
	if (id < 0)
		id = 0;

It's not as pretty, but it is a limitation of how of_property_read_u32
has to be implemented.  I hope to find a better way to do it that
doesn't have the u32 restriction on the return value.

g.


> 
> This condition should prevents value to be less than zero, but is
> does not. It's because type, which is u32 few lines before,
> condition is never true.  So I suggest changing it to int. Actually,
> there was patch some time ago, which has changed it into u32 (last
> patch for xsysace.c).
> 
> 	http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=5d10302f46df1d9a85c34ea97f9b6c29e414482e
> 
> And finally here is my patch, which suggests changing this line back:
> 
> Test for signed value is never true, because of unsigned type.
> 
> From: Petr Cvek <petr.cvek@....cz>
> 
> Signed-off-by: Petr Cvek <petr.cvek@....cz>
> ---
> diff --git a/drivers/block/xsysace.c b/drivers/block/xsysace.c
> index fb1975d..3ed920c 100644
> --- a/drivers/block/xsysace.c
> +++ b/drivers/block/xsysace.c
> @@ -1155,7 +1155,7 @@ static int __devinit ace_probe(struct
> platform_device *dev)
>    {
>           resource_size_t physaddr = 0;
>           int bus_width = ACE_BUS_WIDTH_16; /* FIXME: should not be hard
> coded */
> -       u32 id = dev->id;
> +       int id = dev->id;
>           int irq = NO_IRQ;
>           int i;
> 
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