linux-kernel - Re: [PATCH -next] drm/panthor: Use the BITS_PER

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Message-ID: <33ff88fc-0372-48ed-b66e-85841eda83aa@arm.com>
Date: Mon, 2 Sep 2024 10:23:08 +0100
From: Steven Price <steven.price@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, boris.brezillon@...labora.com,
 liviu.dudau@....com, maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
 tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] drm/panthor: Use the BITS_PER_LONG macro

On 31/08/2024 03:45, Jinjie Ruan wrote:
> sizeof(unsigned long) * 8 is the number of bits in an unsigned long
> variable, replace it with BITS_PER_LONG macro to make them simpler.
> 
> And fix the warning:
> 	WARNING: Comparisons should place the constant on the right side of the test
> 	#23: FILE: drivers/gpu/drm/panthor/panthor_mmu.c:2696:
> 	+       if (BITS_PER_LONG < va_bits) {
> 
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index d47972806d50..2a0c46391374 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -2693,7 +2693,7 @@ int panthor_mmu_init(struct panthor_device *ptdev)
>  	 * which passes iova as an unsigned long. Patch the mmu_features to reflect this
>  	 * limitation.
>  	 */
> -	if (sizeof(unsigned long) * 8 < va_bits) {
> +	if (va_bits > BITS_PER_LONG) {
>  		ptdev->gpu_info.mmu_features &= ~GENMASK(7, 0);
>  		ptdev->gpu_info.mmu_features |= sizeof(unsigned long) * 8;

Can you fix this to BITS_PER_LONG too? Since this code is clamping the
value in mmu_features it looks really odd to have the new value written
differently to the test in the 'if' statement.

Also, a minor point, but the "-next" tag in the subject is
pointless/confusing - this code is in mainline already (merged for
v6.10-rc1).

Thanks,
Steve