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Date: Wed, 28 Feb 2024 09:32:01 -0600
From: Lucas De Marchi <lucas.demarchi@intel.com>
To: Arnd Bergmann <arnd@kernel.org>
CC: Oded Gabbay <ogabbay@kernel.org>, Thomas =?utf-8?Q?Hellstr=C3=B6m?=
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Subject: Re: [PATCH 2/3] [v2] drm/xe/mmio: fix build warning for BAR resize
 on 32-bit
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References: <20240226124736.1272949-1-arnd@kernel.org>
 <20240226124736.1272949-2-arnd@kernel.org>
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On Mon, Feb 26, 2024 at 01:46:37PM +0100, Arnd Bergmann wrote:
>From: Arnd Bergmann <arnd@arndb.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: 237412e45390 ("drm/xe: Enable 32bits build")
>Signed-off-by: Arnd Bergmann <arnd@arndb.de>


Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>

Lucas De Marchi

>---
>v2: use correct Fixes tag
>---
> 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
>