From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B13FDC48BD4 for ; Tue, 25 Jun 2019 14:12:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8ED91208E3 for ; Tue, 25 Jun 2019 14:12:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729517AbfFYOMV (ORCPT ); Tue, 25 Jun 2019 10:12:21 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:53027 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727070AbfFYOMU (ORCPT ); Tue, 25 Jun 2019 10:12:20 -0400 Received: from kresse.hi.pengutronix.de ([2001:67c:670:100:1d::2a]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1hfmBE-0004Im-Hb; Tue, 25 Jun 2019 16:12:16 +0200 Message-ID: <1561471935.2587.11.camel@pengutronix.de> Subject: Re: [PATCH] drm/amd/display: Use msleep instead of udelay for 8ms wait From: Lucas Stach 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 Date: Tue, 25 Jun 2019 16:12:15 +0200 In-Reply-To: <20190625140046.31682-1-harry.wentland@amd.com> References: <20190625140046.31682-1-harry.wentland@amd.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6-1+deb9u1 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::2a X-SA-Exim-Mail-From: l.stach@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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);