linux-kernel - Re: [PATCH] gpu: drm: msm: Replace type of paddr to uint32

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Date:	Thu, 5 Jun 2014 10:49:27 -0400
From:	Rob Clark <robdclark@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"Matwey V. Kornilov" <matwey@....msu.ru>,
	David Brown <davidb@...eaurora.org>,
	Daniel Walker <dwalker@...o99.com>,
	Bryan Huntsman <bryanh@...eaurora.org>,
	David Airlie <airlied@...ux.ie>, linux-arm-msm@...r.kernel.org,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	matwey.kornilov@...il.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpu: drm: msm: Replace type of paddr to uint32_t.

On Thu, Jun 5, 2014 at 3:24 AM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Thu, Jun 5, 2014 at 2:05 AM, Rob Clark <robdclark@...il.com> wrote:
>> On Wed, Jun 4, 2014 at 6:54 AM, Matwey V. Kornilov <matwey@....msu.ru> wrote:
>>> From e7147352639fd8f92b1cc85cff9bc5046c7a2130 Mon Sep 17 00:00:00 2001
>>> From: "Matwey V. Kornilov" <matwey.kornilov@...il.com>
>>> Date: Mon, 2 Jun 2014 20:17:29 +0400
>>> Subject: [PATCH] Replace type of paddr to uint32_t.
>>>
>>> This patch helps to avoid the following build issue:
>>>
>>> drivers/gpu/drm/msm/msm_fbdev.c:108:2: error: passing argument 3 of
>>> 'msm_gem_get_iova_locked' from incompatible pointer type [-Werror]
>>>   msm_gem_get_iova_locked(fbdev->bo, 0, &paddr);
>>>   ^
>>> In file included from drivers/gpu/drm/msm/msm_fbdev.c:18:0:
>>> drivers/gpu/drm/msm/msm_drv.h:153:5: note: expected 'uint32_t *' but
>>> argument is of type 'dma_addr_t *'
>>>  int msm_gem_get_iova_locked(struct drm_gem_object *obj, int id,
>>>      ^
>>>
>>> Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
>>
>> Reviewed-by: Rob Clark <robdclark@...il.com>
>
> Perhaps the uint32_t should become dma_addr_t instead?
>
> drivers/gpu/drm/msm/msm_gem.h has:
>
>         struct {
>                 // XXX
>                 uint32_t iova;
>         } domain[NUM_DOMAINS];
>
> (note the "XXX").

the "XXX" is actually for missing refcnting for pin cnt (so we can
know when it is safe to unpin buffers), which I've not had time to add
yet (but is not needed yet).

On the gpu side of things, it will be another big hw change before 64b
hw (ie. the existing code that deals w/ existing registers won't be
shared, I don't think).  On display side, I'm less sure, but there
isn't currently room to expand base address registers to 64bit without
shuffling a fair bit of registers around, so again probably will be a
new back-end for 64b display controller.

The GEM code would still be shared, so may need to support 64b some
day..  possibly that has to switch over to dma_addr_t and then
downcast to u32 in the mdp/adreno hw generation specific backend code.
 But there is at least one more generation of hw before I have to
worry about that ;-)

BR,
-R

>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
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