From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752100AbdHDGuR (ORCPT ); Fri, 4 Aug 2017 02:50:17 -0400 Received: from smtp.domeneshop.no ([194.63.252.55]:60509 "EHLO smtp.domeneshop.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751284AbdHDGuP (ORCPT ); Fri, 4 Aug 2017 02:50:15 -0400 Subject: Re: [PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access To: David Lechner , 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> From: =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= Message-ID: <8954ef28-26dc-df6c-014c-34b0ce5fdbfb@tronnes.org> Date: Fri, 4 Aug 2017 08:49:52 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <51efe719-566f-6761-9b39-c4cdfdba7a3c@lechnology.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Noralf.