linux-kernel - Re: [PATCH 5/7] drm/sun4i: backend: Offset layer buffer address by DRAM starting address

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Message-ID: <20171016080043.xqpcxj7xfckcxdem@flea.lan>
Date:   Mon, 16 Oct 2017 10:00:43 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH 5/7] drm/sun4i: backend: Offset layer buffer address by
 DRAM starting address

Hi,

I've applied all the other patches.

On Sat, Oct 14, 2017 at 12:02:50PM +0800, Chen-Yu Tsai wrote:
> The display backend, as well as other peripherals that have a DRAM
> clock gate and access DRAM directly, bypassing the system bus,
> address the DRAM starting from 0x0, while physical addresses the
> system uses starts from 0x40000000 (or 0x20000000 in A80's case).
> 
> Correct the address configured into the backend layer registers
> by PHYS_OFFSET to account for this.

However, I'm a bit confused at this.

The driver has been working so far, which it wouldn't have been able
to if the address was wrong. How was this problem noticed, and how can
that fix not be an issue in itself?

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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