[PATCH 12/21] drm/tilcdc: Allow build without __iowmb()

[Tomi Valkeinen]

On 10/04/2024 20:04, Ville Syrjälä wrote:
> On Wed, Apr 10, 2024 at 06:25:17PM +0300, 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 at linux.intel.com>
>>>>
>>>> __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 at iki.fi>
>>>> Cc: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
>>>> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
>>>> ---
>>>>    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.
> 
> What if someone tries to actually boot a kernel built
> with COMPILE_TEST=y on a machine with this hardware?

Ah, right...

#ifndef __iowmb
#define __iowmb BUG
#endif

? =)

Maybe go with the original one, but with a comment like "allow 
compilation without __iowmb() for COMPILE_TEST" or such.

  Tomi