On 10/04/2024 18:25, Ville Syrjälä wrote:
On Wed, Apr 10, 2024 at 12:06:29PM +0300, Tomi Valkeinen wrote:
On 08/04/2024 20:04, Ville Syrjala wrote:
From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
__iowmb() isn't available on most architectures. Make
its use optional so that the driver can be built on
other architectures with COMPILE_TEST=y.
Cc: Jyri Sarha <jyri.sarha@xxxxxx>
Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/tilcdc/tilcdc_regs.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/gpu/drm/tilcdc/tilcdc_regs.h b/drivers/gpu/drm/tilcdc/tilcdc_regs.h
index f90e2dc3457c..44e4ada30fba 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_regs.h
+++ b/drivers/gpu/drm/tilcdc/tilcdc_regs.h
@@ -125,7 +125,9 @@ static inline void tilcdc_write64(struct drm_device *dev, u32 reg, u64 data)
#if defined(iowrite64) && !defined(iowrite64_is_nonatomic)
iowrite64(data, addr);
#else
+#ifdef __iowmb
__iowmb();
+#endif
/* This compiles to strd (=64-bit write) on ARM7 */
*(volatile u64 __force *)addr = __cpu_to_le64(data);
#endif
As the memory barrier is an important part there, would it be better to
ifdef based on COMPILE_TEST, to make it clear why it's being done?
I can do that if you prefer.
I suppose the real question is why iowrite64() doesn't work
if a hand rolled version does work?
If I recall right, there is (was?) no iowrite64. The bus is 32 bit
anyway. But the two 32 bit registers written with the tilcdc_write64()
have an annoying HW race, so we tried to find a method of writing them
that reduces the chance of race to a minimum.
Tomi
