Re: [PATCHv5 1/4] arm64: io: Use asm-generic high level MMIO accessors

On 12/6/2021 2:20 PM, Arnd Bergmann wrote:

On Mon, Dec 6, 2021 at 9:28 AM Sai Prakash Ranjan
[off-list ref] wrote:

quoted

Remove custom arm64 MMIO accessors read{b,w,l,q} and their relaxed
versions in support to use asm-generic ones. Also define arm64
barrier macros to override the asm-generic defined barriers.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sai Prakash Ranjan <redacted>

This looks correct, but I would change one detail:

quoted

+#define __io_ar(v)             __io_par(v)
+#define __io_bw()              __iowmb()
+#define __io_br(v)
+#define __io_aw(v)

The default __io_par() is defined in terms of __io_ar(), so it would
be more logical
to remove the custom __io_par() and just define __io_ar() here.

Makes sense, will do this.

I think it would be even better to flip these around and make the low-level
definitions __io_ar() and __io_bw(), and then defining the arm64 specific
macros based on those:

/* arm64-specific, don't use in portable drivers */
#define __iormb(v)     __io_ar(v)
#define __iowmb()      __io_bw()
#define __iomb()        dma_mb()

So __iormb on arm64 has some dummy control dependency stuff as well based on
("arm64: io: Ensure calls to delay routines are ordered against prior 
readX()") and then we would
need to change __iormb definition to __io_ar which doesn't seem like 
__iormb definition to be exact
right?

Thanks,
Sai

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel