linux-kernel - Re: [PATCH 3/3] rtc: optee: simplify OP-TEE context match

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Message-ID: <e05ccdce1e82b42e837d104922eec1600cce579d.camel@linaro.org>
Date: Fri, 30 Jan 2026 16:03:37 +0100
From: Rouven Czerwinski <rouven.czerwinski@...aro.org>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: Jens Wiklander <jens.wiklander@...aro.org>, Sumit Garg
	 <sumit.garg@...nel.org>, Olivia Mackall <olivia@...enic.com>, Herbert Xu
	 <herbert@...dor.apana.org.au>, Clément Léger
	 <clement.leger@...tlin.com>, op-tee@...ts.trustedfirmware.org, 
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org, 
	linux-rtc@...r.kernel.org
Subject: Re: [PATCH 3/3] rtc: optee: simplify OP-TEE context match

Hi Alexandre,

On Thu, 2026-01-29 at 17:05 +0100, Alexandre Belloni wrote:
> On 26/01/2026 11:11:26+0100, Rouven Czerwinski via B4 Relay wrote:
> > From: Rouven Czerwinski <rouven.czerwinski@...aro.org>
> > 
> > Simplify the TEE implementor ID match by returning the boolean
> > expression directly instead of going through an if/else.
> > 
> > Signed-off-by: Rouven Czerwinski <rouven.czerwinski@...aro.org>
> > ---
> >  drivers/rtc/rtc-optee.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/drivers/rtc/rtc-optee.c b/drivers/rtc/rtc-optee.c
> > index 184c6d142801..2f18be3de684 100644
> > --- a/drivers/rtc/rtc-optee.c
> > +++ b/drivers/rtc/rtc-optee.c
> > @@ -541,10 +541,7 @@ static int optee_rtc_read_info(struct device
> > *dev, struct rtc_device *rtc,
> >  
> >  static int optee_ctx_match(struct tee_ioctl_version_data *ver,
> > const void *data)
> >  {
> > -	if (ver->impl_id == TEE_IMPL_ID_OPTEE)
> > -		return 1;
> > -	else
> > -		return 0;
> > +	return (ver->impl_id == TEE_IMPL_ID_OPTEE);
> 
> I guess the correct way to do this would be:
> 
> return !!(ver->impl_id == TEE_IMPL_ID_OPTEE);

Could you explain why? If I read the standard correctly, an equality
operation always produces either 1 or 0, so there should be no need for
!! here like there is for bit flag comparisons, i.e. !!(flag &
SOME_FLAG_SET) to normalize to 1 or 0. Wondering if I am missing
something.

> But is this change actually generating better code?
> 
> Before:
> 
> static int optee_ctx_match(struct tee_ioctl_version_data *ver, const
> void *data)
> {
>         if (ver->impl_id == TEE_IMPL_ID_OPTEE)
>        0:       e5900000        ldr     r0, [r0]
>                 return 1;
>         else
>                 return 0;
> }
>        4:       e2400001        sub     r0, r0, #1
>        8:       e16f0f10        clz     r0, r0
>        c:       e1a002a0        lsr     r0, r0, #5
>       10:       e12fff1e        bx      lr
> 
> After:
> 
> static int optee_ctx_match(struct tee_ioctl_version_data *ver, const
> void *data)
> {
>         return !!(ver->impl_id == TEE_IMPL_ID_OPTEE);
>        0:       e5900000        ldr     r0, [r0]
> }
>        4:       e2400001        sub     r0, r0, #1
>        8:       e16f0f10        clz     r0, r0
>        c:       e1a002a0        lsr     r0, r0, #5
>       10:       e12fff1e        bx      lr
> 
> I'm in favor of keeping the current version.

I like the short version better, but I am also not very attached to
getting this in at all, I'll let the maintainers decide.

Thanks and best regards,
Rouven