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Date:   Tue, 10 Oct 2023 15:22:56 +0200
From:   Thierry Reding <thierry.reding@gmail.com>
To:     Sui Jingfeng <suijingfeng@loongson.cn>
Cc:     Mikko Perttunen <mperttunen@nvidia.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        dri-devel@lists.freedesktop.org, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] drm/tegra: Return an error code if fails
Message-ID: <ZSVQMPuRnXzC0lgf@orome.fritz.box>
References: <20230626143331.640454-1-suijingfeng@loongson.cn>
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On Mon, Jun 26, 2023 at 10:33:30PM +0800, Sui Jingfeng wrote:
> Return -ENOMEM if tegra_bo_mmap() fails.
>=20
> Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
> ---
>  drivers/gpu/drm/tegra/gem.c | 2 ++
>  1 file changed, 2 insertions(+)

Sorry, this fell through the cracks. I think it'd be better if
tegra_bo_mmap() were to be improved to always return either an ERR_PTR()
encoded error code or a valid pointer. Throwing NULL into the mix isn't
useful because it typically means something like -ENOMEM anyway. Error
codes are more explicit, so since we're already using them for some
cases, might as well return them for all.

Actually, looks like tegra_bo_mmap() never actually returns an ERR_PTR()
encoded error code. It's either obj->vaddr, the return value of vmap()
(which is either NULL or the address of the mapping), or the address
obtained from dma_buf_vmap_unlocked() (i.e. map.vaddr) or NULL on
failure. So I think it would equally make sense to keep your patch and
to remove the IS_ERR() check below it.

I would slightly prefer the first option, but either is fine.

Thierry

> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index dea38892d6e6..0ce22935fbd3 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -710,6 +710,8 @@ static int tegra_gem_prime_vmap(struct dma_buf *buf, =
struct iosys_map *map)
>  	void *vaddr;
> =20
>  	vaddr =3D tegra_bo_mmap(&bo->base);
> +	if (!vaddr)
> +		return -ENOMEM;
>  	if (IS_ERR(vaddr))
>  		return PTR_ERR(vaddr);
> =20
> --=20
> 2.25.1
>=20

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