linux-kernel - Re: [PATCH v1 1/8] drm/etnaviv: Using the size

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Date:   Mon, 17 Jul 2023 11:43:23 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Sui Jingfeng <sui.jingfeng@...ux.dev>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     loongson-kernel@...ts.loongnix.cn,
        Sui Jingfeng <suijingfeng@...ngson.cn>,
        etnaviv@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/8] drm/etnaviv: Using the size_t variable to store
 the number of pages

Hi Jingfeng,

Am Freitag, dem 23.06.2023 um 18:08 +0800 schrieb Sui Jingfeng:
> From: Sui Jingfeng <suijingfeng@...ngson.cn>
> 
> Because the etnaviv_gem_new_private() function receives the size_t argument
> for the number of pages. And the number of pages should be unsigned.
> 
> Note that Most 32-bit architectures use "unsigned int" size_t,
> and all 64-bit architectures use "unsigned long" size_t.
> So, let's keep the argument and parameter consistent.
> 
This explanation doesn't add up. npages is just that: a number of
pages. Why would it make sense to use size_t here?

If you want to be consistent I would have expected this change to
switch things to unsigned int, as you did in the second patch of this
series.

Regards,
Lucas

> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> index 3524b5811682..b003481adc2b 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> @@ -114,7 +114,8 @@ struct drm_gem_object *etnaviv_gem_prime_import_sg_table(struct drm_device *dev,
>  {
>  	struct etnaviv_gem_object *etnaviv_obj;
>  	size_t size = PAGE_ALIGN(attach->dmabuf->size);
> -	int ret, npages;
> +	size_t npages = size / PAGE_SIZE;
> +	int ret;
>  
>  	ret = etnaviv_gem_new_private(dev, size, ETNA_BO_WC,
>  				      &etnaviv_gem_prime_ops, &etnaviv_obj);
> @@ -123,8 +124,6 @@ struct drm_gem_object *etnaviv_gem_prime_import_sg_table(struct drm_device *dev,
>  
>  	lockdep_set_class(&etnaviv_obj->lock, &etnaviv_prime_lock_class);
>  
> -	npages = size / PAGE_SIZE;
> -
>  	etnaviv_obj->sgt = sgt;
>  	etnaviv_obj->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
>  	if (!etnaviv_obj->pages) {