[PATCH] efi: rtc-efi: mark UIE as unsupported

[PATCH] efi: rtc-efi: mark UIE as unsupported

[Ard Biesheuvel]

Tools like hwclock attempt to enable the RTC update interrupt (UIE) to
maximize the accuracy of the reported time value. The EFI rtc does not
have interrupt capability so this is a pointless exercise to begin with,
but the generic RTC framework ends up issuing a SetWakeupTime() Runtime
Services call before drawing that conclusion on its own.

Instead, we can mark UIE as unsupported at driver probe time. The net
result is the same, but without the spurious SetWakeupTime() call.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
---
 drivers/rtc/rtc-efi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
index b37b0c80bd5a..cb989cd00b14 100644
--- a/drivers/rtc/rtc-efi.c
+++ b/drivers/rtc/rtc-efi.c
@@ -218,6 +218,7 @@ static int __init efi_rtc_probe(struct platform_device *dev)
 	if (IS_ERR(rtc))
 		return PTR_ERR(rtc);
 
+	rtc->uie_unsupported = 1;
 	platform_set_drvdata(dev, rtc);
 
 	return 0;
-- 
1.8.3.2

Re: [PATCH] efi: rtc-efi: mark UIE as unsupported

[Matt Fleming]

On Tue, 13 Jan, at 12:28:53PM, Ard Biesheuvel wrote:
> Tools like hwclock attempt to enable the RTC update interrupt (UIE) to
> maximize the accuracy of the reported time value. The EFI rtc does not
> have interrupt capability so this is a pointless exercise to begin with,
> but the generic RTC framework ends up issuing a SetWakeupTime() Runtime
> Services call before drawing that conclusion on its own.
> 
> Instead, we can mark UIE as unsupported at driver probe time. The net
> result is the same, but without the spurious SetWakeupTime() call.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  drivers/rtc/rtc-efi.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
> index b37b0c80bd5a..cb989cd00b14 100644
> --- a/drivers/rtc/rtc-efi.c
> +++ b/drivers/rtc/rtc-efi.c
> @@ -218,6 +218,7 @@ static int __init efi_rtc_probe(struct platform_device *dev)
>  	if (IS_ERR(rtc))
>  		return PTR_ERR(rtc);
>  
> +	rtc->uie_unsupported = 1;
>  	platform_set_drvdata(dev, rtc);
>  
>  	return 0;

Looks fine to me. Picked up in the EFI tree for v3.20. Thanks Ard.

-- 
Matt Fleming, Intel Open Source Technology Center