[PATCH 21/21] dma-mapping: replace custom code with generic implementation

Arnd Bergmann arnd at arndb.de
Sat Apr 1 00:04:23 AEDT 2023

On Tue, Mar 28, 2023, at 00:25, Christoph Hellwig wrote:
>> +static inline void arch_dma_cache_wback(phys_addr_t paddr, size_t size)
>>  {
>> +	dma_cache_wback(paddr, size);
>> +}
>> +static inline void arch_dma_cache_inv(phys_addr_t paddr, size_t size)
>> +{
>> +	dma_cache_inv(paddr, size);
>>  }
>> +static inline void arch_dma_cache_wback_inv(phys_addr_t paddr, size_t size)
>>  {
>> +	dma_cache_wback_inv(paddr, size);
>> +}
> There are the only calls for the three functions for each of the
> involved functions.  So I'd rather rename the low-level symbols
> (and drop the pointless exports for two of them) rather than adding
> these wrapppers.
> The same is probably true for many other architectures.

Ok, done that now.

>> +static inline bool arch_sync_dma_clean_before_fromdevice(void)
>> +{
>> +	return false;
>> +}
>> +static inline bool arch_sync_dma_cpu_needs_post_dma_flush(void)
>> +{
>> +	return true;
>>  }
> Is there a way to cut down on this boilerplate code by just having
> sane default, and Kconfig options to override them if they are not
> runtime decisions?

I've changed arch_sync_dma_clean_before_fromdevice() to a
Kconfig symbol now, as this is never a runtime decision.

For arch_sync_dma_cpu_needs_post_dma_flush(), I have this
version now in common code, which lets mips and arm have
their own logic and has the same effect elsewhere:

+#ifndef arch_sync_dma_cpu_needs_post_dma_flush
+static inline bool arch_sync_dma_cpu_needs_post_dma_flush(void)

>> +#include <linux/dma-sync.h>
> I can't really say I like the #include version here despite your
> rationale in the commit log.  I can probably live with it if you
> think it is absolutely worth it, but I'm really not in favor of it.
>> +	def_bool y
> What do we need this symbol for?  Unless I'm missing something it is
> always enable for arm32, and only used in arm32 code.

This was left over from an earlier draft and accidentally duplicates
the thing that I have in the Arm version for the existing
ARCH_HAS_DMA_MARK_CLEAN. I dropped this one and the
generic copy of the arch_dma_mark_dcache_clean() function
now, but still need to revisit the arm version, as it sounds
like it has slightly different semantics from the ia64 version.


More information about the Linuxppc-dev mailing list