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Date:   Tue, 10 Oct 2023 17:31:33 +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: <ZSVuVcqdGfGtQIQj@orome.fritz.box>
References: <20230626143331.640454-1-suijingfeng@loongson.cn>
 <ZSVQMPuRnXzC0lgf@orome.fritz.box>
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On Tue, Oct 10, 2023 at 03:22:56PM +0200, Thierry Reding wrote:
> 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(+)
>=20
> 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.
>=20
> 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.
>=20
> I would slightly prefer the first option, but either is fine.

How about the attached patch?

Thierry

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=46rom b34a09efcf7b1d2c25d3baf8c6d91c5ca09b4e0f Mon Sep 17 00:00:00 2001
=46rom: Thierry Reding <treding@nvidia.com>
Date: Tue, 10 Oct 2023 17:26:14 +0200
Subject: [PATCH] drm/tegra: gem: Do not return NULL in tegra_bo_mmap()

It's confusing for a function to return NULL and ERR_PTR()-encoded error
codes on failure. Make sure we only ever return the latter since that's
what callers already expect.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
 drivers/gpu/drm/tegra/gem.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 11296de59c5a..679460e05c05 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -178,6 +178,7 @@ static void *tegra_bo_mmap(struct host1x_bo *bo)
 {
 	struct tegra_bo *obj =3D host1x_to_tegra_bo(bo);
 	struct iosys_map map;
+	void *vaddr;
 	int ret;
=20
 	if (obj->vaddr)
@@ -185,10 +186,18 @@ static void *tegra_bo_mmap(struct host1x_bo *bo)
=20
 	if (obj->gem.import_attach) {
 		ret =3D dma_buf_vmap_unlocked(obj->gem.import_attach->dmabuf, &map);
-		return ret ? NULL : map.vaddr;
+		if (ret < 0)
+			return ERR_PTR(ret);
+
+		return map.vaddr;
 	}
=20
-	return vmap(obj->pages, obj->num_pages, VM_MAP, pgprot_writecombine(PAGE_=
KERNEL));
+	vaddr =3D vmap(obj->pages, obj->num_pages, VM_MAP,
+		     pgprot_writecombine(PAGE_KERNEL));
+	if (!vaddr)
+		return -ENOMEM;
+
+	return vaddr;
 }
=20
 static void tegra_bo_munmap(struct host1x_bo *bo, void *addr)
--=20
2.42.0


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