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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E5A24C43387 for ; Sat, 12 Jan 2019 12:01:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A9FF520870 for ; Sat, 12 Jan 2019 12:01:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726412AbfALMBB (ORCPT ); Sat, 12 Jan 2019 07:01:01 -0500 Received: from asavdk3.altibox.net ([109.247.116.14]:41654 "EHLO asavdk3.altibox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725823AbfALMBB (ORCPT ); Sat, 12 Jan 2019 07:01:01 -0500 Received: from ravnborg.org (unknown [158.248.194.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by asavdk3.altibox.net (Postfix) with ESMTPS id 1982A20054; Sat, 12 Jan 2019 13:00:57 +0100 (CET) Date: Sat, 12 Jan 2019 13:00:56 +0100 From: Sam Ravnborg To: Jagan Teki Cc: David Airlie , linux-amarula@amarulasolutions.com, linux-kernel , dri-devel , Thierry Reding , Michael Trimarchi , Sean Paul Subject: Re: [PATCH V7 2/2] drm/panel: Add Sitronix ST7701 panel driver Message-ID: <20190112120056.GA7374@ravnborg.org> References: <20190111124714.19566-1-jagan@amarulasolutions.com> <20190111124714.19566-2-jagan@amarulasolutions.com> <20190111211931.GA29735@ravnborg.org> <20190112101409.GA14273@ravnborg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-CMAE-Score: 0 X-CMAE-Analysis: v=2.3 cv=dqr19Wo4 c=1 sm=1 tr=0 a=UWs3HLbX/2nnQ3s7vZ42gw==:117 a=UWs3HLbX/2nnQ3s7vZ42gw==:17 a=kj9zAlcOel0A:10 a=h2XvLM43PzkowCm6i1cA:9 a=CjuIK1q_8ugA:10 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > > > > > + > > > > > + msleep(st7701->sleep_delay); > > > > > + > > > > > + gpiod_set_value(st7701->reset, 0); > > > > > + > > > > > + gpiod_set_value(st7701->reset, 1); > > > > > + > > > > > + gpiod_set_value(st7701->reset, 0); > > > > No timing constrains here? In prepare there are sleeps intermixed. > > > > > > Delay while doing unprare is not needed I suppose. > > > > If the purpose is alone to reset the display then a single write '0' > > should do it I think > > I even tried this just set 0, since prepare is doing a sequence, it > good behavior to do the reverse during handoff. ie reason I just > initiated this sequence. > > > And there is a requirement that it must be low for a minimum of 10 us > > which would be good to have here. > > Sorry, I didn't get this requirement what is this for? The st7701 will ignore reset pulse shorter than 10 us - see Trw in table 9 reset timing (page 54). But as we just assert reset (set it to 0), this timing constraint can be ignored. > > I aslo found in chapter 9. (page 163 - second line) this statement: > > "VDDA and VDDI must be powered down with minimum 120msec." > > Yes unprepare is doing the same, it exit from sleep out mode and wait > for 120msec and do the reset. > > > > > This is similar to the unprepare delay to be found in simple-panel.c > > So an unprepare delay seems in order here. > > Look like simple-panel.c is doing delay after reset initiated and > regulator disabled. Sam