From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lucas Stach Subject: Re: [PATCH] drm/amd/display: Use msleep instead of udelay for 8ms wait Date: Tue, 25 Jun 2019 16:12:15 +0200 Message-ID: <1561471935.2587.11.camel@pengutronix.de> References: <20190625140046.31682-1-harry.wentland@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190625140046.31682-1-harry.wentland@amd.com> Sender: linux-kernel-owner@vger.kernel.org To: Harry Wentland , airlied@gmail.com, natechancellor@gmail.com Cc: sunpeng.li@amd.com, Anthony.Koo@amd.com, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, alexander.deucher@amd.com, Jun.Lei@amd.com, Bhawanpreet.Lakha@amd.com, christian.koenig@amd.com List-Id: amd-gfx.lists.freedesktop.org Hi Harry, Am Dienstag, den 25.06.2019, 10:00 -0400 schrieb Harry Wentland: > arm32's udelay only allows values up to 2000 microseconds. msleep > does the trick for us here as there is no problem if this isn't > microsecond accurate and takes a tad longer. A "tad" longer in this case means likely double the intended wait. Please see "SLEEPING FOR ~USECS OR SMALL MSECS ( 10us - 20ms)" in Documentation/timers/timers-howto.txt. The sleep here should use usleep_range. In general the DC code seems to use quite a lot of the udelay busy waits. I doubt that many of those occurrences are in atomic context, so could easily use a sleeping wait. Digging further this seems to apply across amdgpu, not only DC. Regards, Lucas > Signed-off-by: Harry Wentland > --- >  drivers/gpu/drm/amd/display/dc/core/dc_link.c | 2 +- >  1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c > b/drivers/gpu/drm/amd/display/dc/core/dc_link.c > index 4c31930f1cdf..f5d02f89b3f9 100644 > --- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c > +++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c > @@ -548,7 +548,7 @@ static void > read_edp_current_link_settings_on_detect(struct dc_link *link) >   break; >   } >   > - udelay(8000); > + msleep(8); >   } >   >   ASSERT(status == DC_OK);