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RE: [PATCH] xen/arm: debug-pl011: Use 32-bit accessors for broader compatibility
- To: Michal Orzel <michal.orzel@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Thu, 1 Jun 2023 09:03:37 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
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- Thread-topic: [PATCH] xen/arm: debug-pl011: Use 32-bit accessors for broader compatibility
Hi Michal,
> -----Original Message-----
> Subject: [PATCH] xen/arm: debug-pl011: Use 32-bit accessors for broader
> compatibility
>
> There are implementations of the PL011 that can only handle 32-bit
> accesses (i.e. no 16-bit or 8-bit), usually advertised by 'reg-io-width'
> dt property set to 4. On such UARTs, the current early printk code for
> arm64 does not work. To fix this issue, make all the accesses to be 32-bit
> by using ldr, str without a size field. This makes it possible to use
> early printk on such platforms, while all the other implementations should
> generally cope with 32-bit accesses. In case they do not, they would
> already fail as we explicitly use writel/readl in the runtime driver to
> maintain broader compatibility and to be SBSAv2 compliant. Therefore, this
> change makes the runtime/early handling consistent (also it matches the
> arm32 debug-pl011 code).
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Reviewed-by: Henry Wang <Henry.Wang@xxxxxxx>
Kind regards,
Henry
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