linux-kernel - [PATCH 5.4 049/434] drm: Use EOPNOTSUPP, not ENOTSUPP

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Date:   Sun, 29 Dec 2019 18:21:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        José Roberto de Souza <jose.souza@...el.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sean Paul <sean@...rly.run>,
        Alex Deucher <alexander.deucher@....com>,
        Andres Rodriguez <andresx7@...il.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 049/434] drm: Use EOPNOTSUPP, not ENOTSUPP

From: Daniel Vetter <daniel.vetter@...ll.ch>

[ Upstream commit c7581a414d28413c1dd6d116d44859b5a52e0950 ]

- it's what we recommend in our docs:

https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#recommended-ioctl-return-values

- it's the overwhelmingly used error code for "operation not
  supported", at least in drm core (slightly less so in drivers):

$ git grep EOPNOTSUPP -- drivers/gpu/drm/*c | wc -l
83
$ git grep ENOTSUPP -- drivers/gpu/drm/*c | wc -l
5

- include/linux/errno.h makes it fairly clear that these are for nfsv3
  (plus they also have error codes above 512, which is the block with
  some special behaviour ...)

/* Defined for the NFSv3 protocol */

If the above isn't reflecting current practice, then I guess we should
at least update the docs.

Noralf commented:

Ben Hutchings made this comment[1] in a thread about use of ENOTSUPP in
drivers:

  glibc's strerror() returns these strings for ENOTSUPP and EOPNOTSUPP
  respectively:

  "Unknown error 524"
  "Operation not supported"

So at least for errors returned to userspace EOPNOTSUPP makes sense.

José asked:

> Hopefully this will not break any userspace

None of the functions in drm_edid.c affected by this reach userspace,
it's all driver internal.

Same for the mipi function, that error code should be handled by
drivers. Drivers are supposed to remap "the hw is on fire" to EIO when
reporting up to userspace, but I think if a driver sees this it would
be a driver bug.
v2: Augment commit message with comments from Noralf and José

Reviewed-by: José Roberto de Souza <jose.souza@...el.com>
Acked-by: Noralf Trønnes <noralf@...nnes.org>
Cc: José Roberto de Souza <jose.souza@...el.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc: Maxime Ripard <mripard@...nel.org>
Cc: Sean Paul <sean@...rly.run>
Cc: Alex Deucher <alexander.deucher@....com>
Cc: Andres Rodriguez <andresx7@...il.com>
Cc: Noralf Trønnes <noralf@...nnes.org>
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190904143942.31756-1-daniel.vetter@ffwll.ch
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/drm_edid.c     | 6 +++---
 drivers/gpu/drm/drm_mipi_dbi.c | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 6b0177112e18..3f50b8865db4 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -3722,7 +3722,7 @@ cea_db_offsets(const u8 *cea, int *start, int *end)
 		if (*end < 4 || *end > 127)
 			return -ERANGE;
 	} else {
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 	}
 
 	return 0;
@@ -4191,7 +4191,7 @@ int drm_edid_to_sad(struct edid *edid, struct cea_sad **sads)
 
 	if (cea_revision(cea) < 3) {
 		DRM_DEBUG_KMS("SAD: wrong CEA revision\n");
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 	}
 
 	if (cea_db_offsets(cea, &start, &end)) {
@@ -4252,7 +4252,7 @@ int drm_edid_to_speaker_allocation(struct edid *edid, u8 **sadb)
 
 	if (cea_revision(cea) < 3) {
 		DRM_DEBUG_KMS("SAD: wrong CEA revision\n");
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 	}
 
 	if (cea_db_offsets(cea, &start, &end)) {
diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
index c4ee2709a6f3..f8154316a3b0 100644
--- a/drivers/gpu/drm/drm_mipi_dbi.c
+++ b/drivers/gpu/drm/drm_mipi_dbi.c
@@ -955,7 +955,7 @@ static int mipi_dbi_typec1_command(struct mipi_dbi *dbi, u8 *cmd,
 	int ret;
 
 	if (mipi_dbi_command_is_read(dbi, *cmd))
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 
 	MIPI_DBI_DEBUG_COMMAND(*cmd, parameters, num);
 
-- 
2.20.1