From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751996AbdHGSA3 (ORCPT ); Mon, 7 Aug 2017 14:00:29 -0400 Received: from vern.gendns.com ([206.190.152.46]:55033 "EHLO vern.gendns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751799AbdHGSA2 (ORCPT ); Mon, 7 Aug 2017 14:00:28 -0400 Subject: Re: [PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access To: =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= , dri-devel@lists.freedesktop.org Cc: David Airlie , linux-kernel@vger.kernel.org References: <1501618466-32191-1-git-send-email-david@lechnology.com> <51efe719-566f-6761-9b39-c4cdfdba7a3c@lechnology.com> <8954ef28-26dc-df6c-014c-34b0ce5fdbfb@tronnes.org> From: David Lechner Message-ID: <4541844e-989c-13fb-0d37-44c39406bd1b@lechnology.com> Date: Mon, 7 Aug 2017 13:00:28 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <8954ef28-26dc-df6c-014c-34b0ce5fdbfb@tronnes.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - vern.gendns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lechnology.com X-Get-Message-Sender-Via: vern.gendns.com: authenticated_id: davidmain+lechnology.com/only user confirmed/virtual account not confirmed X-Authenticated-Sender: vern.gendns.com: davidmain@lechnology.com X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/2017 01:49 AM, Noralf Trønnes wrote: > > Den 04.08.2017 00.41, skrev David Lechner: >> On 08/01/2017 03:14 PM, David Lechner wrote: >>> If we return here and import_attach is true, then >>> dma_buf_end_cpu_access() >>> will not be called balance dma_buf_begin_cpu_access(). >>> >>> Fix by setting ret instead of returning. >>> >>> Signed-off-by: David Lechner >>> --- >>> drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c >>> b/drivers/gpu/drm/tinydrm/mipi-dbi.c >>> index c83eeb7..e10fa4b 100644 >>> --- a/drivers/gpu/drm/tinydrm/mipi-dbi.c >>> +++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c >>> @@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct >>> drm_framebuffer *fb, >>> dev_err_once(fb->dev->dev, "Format is not supported: %s\n", >>> drm_get_format_name(fb->format->format, >>> &format_name)); >>> - return -EINVAL; >>> + ret = -EINVAL; >>> + break; >>> } >>> if (import_attach) >>> >> >> >> I just realized that the next line here can mask ret. >> >> >> if (import_attach) >> ret = dma_buf_end_cpu_access(import_attach->dmabuf, >> DMA_FROM_DEVICE); >> >> So, we should either ignore the return value from >> dma_buf_end_cpu_access() always or add some logic to ignore it if ret >> is already an error. >> >> In some of the other patches I have been sending, we have the same >> situation. I those, I have opted to just ignore the return value from >> dma_buf_end_cpu_access(). e.g... >> >> >> if (import_attach) >> dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE); >> >> Is this a reasonable thing to do? > > mipi_dbi_buf_copy() can be used by other rgb565 controllers, hence > the format check I think. So when that happens, it can be moved to > tinydrm-helpers. > > Currently it's not possible to get an illegal format, since mipi-dbi > only supports those two formats. > Userspace can't set an illegal format, beacuse it's checked: > drm_atomic_commit -> drm_atomic_check_only -> drm_atomic_plane_check -> > drm_plane_check_pixel_format > > So I think we can just leave this alone, or put the check before > import_attach if you really want to put this straight. > I guess we can just leave it alone for now.