linux-kernel - Re: [PATCH 2/3] drm/xe/mmio: fix build warning for BAR resize on 32-bit

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Message-ID: <qybrvc6fwxjnnt4lwuf2xmdbhznvwzz2bhmlm6m57bze65f6xf@rxbkx74kv6k7>
Date: Sun, 25 Feb 2024 21:44:59 -0600
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Arnd Bergmann <arnd@...nel.org>
CC: Oded Gabbay <ogabbay@...nel.org>, Thomas Hellström
	<thomas.hellstrom@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>, "Maarten
 Lankhorst" <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
	<mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
	<airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Nathan Chancellor
	<nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, "Bill
 Wendling" <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, "Rodrigo
 Vivi" <rodrigo.vivi@...el.com>, Matt Roper <matthew.d.roper@...el.com>,
	Matthew Auld <matthew.auld@...el.com>, Matthew Brost
	<matthew.brost@...el.com>, Koby Elbaz <kelbaz@...ana.ai>, "Michael J. Ruhl"
	<michael.j.ruhl@...el.com>, Francois Dugast <francois.dugast@...el.com>, Dave
 Airlie <airlied@...hat.com>, <intel-xe@...ts.freedesktop.org>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
	<llvm@...ts.linux.dev>
Subject: Re: [PATCH 2/3] drm/xe/mmio: fix build warning for BAR resize on
 32-bit

On Sat, Feb 24, 2024 at 01:15:00PM +0100, Arnd Bergmann wrote:
>From: Arnd Bergmann <arnd@...db.de>
>
>clang complains about a nonsensical test on builds with a 32-bit phys_addr_t,
>which means resizing will always fail:
>
>drivers/gpu/drm/xe/xe_mmio.c:109:23: error: result of comparison of constant 4294967296 with expression of type 'resource_size_t' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>  109 |                     root_res->start > 0x100000000ull)
>      |                     ~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~
>
>Previously, BAR resize was always disallowed on 32-bit kernels, but
>this apparently changed recently. Since 32-bit machines can in theory
>support PAE/LPAE for large address spaces, this may end up useful,
>so change the driver to shut up the warning but still work when
>phys_addr_t/resource_size_t is 64 bit wide.
>
>Fixes: 9a6e6c14bfde ("drm/xe/mmio: Use non-atomic writeq/readq variant for 32b")
>Fixes: ea97a66a2218 ("drm/xe: Disable 32bits build")

this second Fixes should not be here? How would "disabling 32bits build"
break 32bits build? I think just the first one is enough, otherwise
237412e45390 ("drm/xe: Enable 32bits build") is your next good
candidate.


Acked-by: Lucas De Marchi <lucas.demarchi@...el.com>

Lucas De Marchi

>Signed-off-by: Arnd Bergmann <arnd@...db.de>
>---
> drivers/gpu/drm/xe/xe_mmio.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_mmio.c b/drivers/gpu/drm/xe/xe_mmio.c
>index e3db3a178760..7ba2477452d7 100644
>--- a/drivers/gpu/drm/xe/xe_mmio.c
>+++ b/drivers/gpu/drm/xe/xe_mmio.c
>@@ -106,7 +106,7 @@ static void xe_resize_vram_bar(struct xe_device *xe)
>
> 	pci_bus_for_each_resource(root, root_res, i) {
> 		if (root_res && root_res->flags & (IORESOURCE_MEM | IORESOURCE_MEM_64) &&
>-		    root_res->start > 0x100000000ull)
>+		    (u64)root_res->start > 0x100000000ul)
> 			break;
> 	}
>
>-- 
>2.39.2
>