linux-kernel - Re: [PATCH] drm/virtio: use %llu format string form atomic64

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Message-ID: <20151007104502.GH21513@n2100.arm.linux.org.uk>
Date:	Wed, 7 Oct 2015 11:45:02 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Dave Airlie <airlied@...hat.com>,
	Gerd Hoffmann <kraxel@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] drm/virtio: use %llu format string form atomic64_t

On Wed, Oct 07, 2015 at 12:41:21PM +0200, Arnd Bergmann wrote:
> The virtgpu driver prints the last_seq variable using the %ld or
> %lu format string, which does not work correctly on all architectures
> and causes this compiler warning on ARM:
> 
> drivers/gpu/drm/virtio/virtgpu_fence.c: In function 'virtio_timeline_value_str':
> drivers/gpu/drm/virtio/virtgpu_fence.c:64:22: warning: format '%lu' expects argument of type 'long unsigned int', but argument 4 has type 'long long int' [-Wformat=]
>   snprintf(str, size, "%lu", atomic64_read(&fence->drv->last_seq));
>                       ^
> drivers/gpu/drm/virtio/virtgpu_debugfs.c: In function 'virtio_gpu_debugfs_irq_info':
> drivers/gpu/drm/virtio/virtgpu_debugfs.c:37:16: warning: format '%ld' expects argument of type 'long int', but argument 3 has type 'long long int' [-Wformat=]
>   seq_printf(m, "fence %ld %lld\n",
>                 ^
> 
> In order to avoid the warnings, this changes the format strings to %llu
> and adds a cast to u64, which makes it work the same way everywhere.

You have to wonder why atomic64_* functions do not use u64 types.
If they're not reliant on manipulating 64-bit quantities, then what's
the point of calling them atomic _64_.

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