linux-kernel - Re: [PATCH 2/3] msm: add minimal board file for HTC Dream device

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Date:	Mon, 16 Nov 2009 08:43:20 -0800
From:	Brian Swetland <swetland@...gle.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Pavel Machek <pavel@....cz>, "Arve Hj?nnev?g" <arve@...roid.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] msm: add minimal board file for HTC Dream device

On Mon, Nov 16, 2009 at 8:36 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Mon, Nov 02, 2009 at 11:49:49AM +0100, Pavel Machek wrote:
>> +MACHINE_START(TROUT, "HTC Dream")
>> +#ifdef CONFIG_MSM_DEBUG_UART
>> +     .phys_io        = MSM_DEBUG_UART_PHYS,
>> +     .io_pg_offst    = ((MSM_DEBUG_UART_BASE) >> 18) & 0xfffc,
>> +#endif
>
> Why is this ifdef'd?  Two reasons why not to do this:
>
> 1. MSM_DEBUG_UART is always defined, so the conditional is pointless

For a default dream build, definitely, but not always on every msm7k
target (some devices may not have a serial port that can safely be
chattered at by the debug code).  For this board file, no harm to
require it.

> 2. the low level page table building code does not expect these to be
>   unset (or even set to an invalid value).  Leaving them unset and
>   having DEBUG_LL enabled is a recipe to prevent booting.

What's the best way to handle a situation where there is no valid
debug uart?  Could the arch/platform require DEBUG_LL be unset via
Kconfig directives if it is configured in a way where there is no
valid debug uart?

> To put it another way, these two fields aren't optional.
>

Thanks,

Brian
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