On Wed, Oct 7, 2015 at 1:23 PM, Arnd Bergmann arnd@arndb.de wrote:
On Wednesday 07 October 2015 13:04:06 Arnd Bergmann wrote:
On Wednesday 07 October 2015 11:45:02 Russell King - ARM Linux wrote:
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_.
I haven't checked all architectures, but I assume what happens is that 64-bit ones just #define atomic64_t atomic_long_t, so they don't have to provide three sets of functions.
scratch that, I just looked at all the architectures and found that it's just completely arbitrary, even within one architecture you get a mix of 'long' and 'long long', plus this gem from MIPS:
static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long u)
which truncates the result to 32 bit.
Woops.
See also my unanswered question in "atomic64 on 32-bit vs 64-bit (was: Re: Add virtio gpu driver.)", which is still valid: https://lkml.org/lkml/2015/6/28/18
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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