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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 752FDC43603 for ; Mon, 16 Dec 2019 13:48:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CED620409 for ; Mon, 16 Dec 2019 13:48:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727972AbfLPNsQ convert rfc822-to-8bit (ORCPT ); Mon, 16 Dec 2019 08:48:16 -0500 Received: from relay6-d.mail.gandi.net ([217.70.183.198]:50891 "EHLO relay6-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727579AbfLPNsP (ORCPT ); Mon, 16 Dec 2019 08:48:15 -0500 X-Originating-IP: 91.224.148.103 Received: from xps13 (unknown [91.224.148.103]) (Authenticated sender: miquel.raynal@bootlin.com) by relay6-d.mail.gandi.net (Postfix) with ESMTPSA id 351A2C0003; Mon, 16 Dec 2019 13:48:11 +0000 (UTC) Date: Mon, 16 Dec 2019 14:48:10 +0100 From: Miquel Raynal To: Maxime Ripard Cc: Thierry Reding , Sam Ravnborg , David Airlie , Daniel Vetter , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Maxime Chevallier , Paul Kocialkowski , Thomas Petazzoni Subject: Re: [PATCH] drm/panel: simple: Support reset GPIOs Message-ID: <20191216144810.18710ed3@xps13> In-Reply-To: <20191216132732.mmqivmpnq4mio6oo@gilmour.lan> References: <20191213181325.26228-1-miquel.raynal@bootlin.com> <20191216130615.qs6ub7bwqofwvhr7@gilmour.lan> <20191216141036.24c22899@xps13> <20191216132732.mmqivmpnq4mio6oo@gilmour.lan> Organization: Bootlin X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sam, Maxime Ripard wrote on Mon, 16 Dec 2019 14:27:32 +0100: > On Mon, Dec 16, 2019 at 02:10:36PM +0100, Miquel Raynal wrote: > > > > drivers/gpu/drm/panel/panel-simple.c | 12 +++++++++++- > > > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c > > > > index 5d487686d25c..15dd495c347d 100644 > > > > --- a/drivers/gpu/drm/panel/panel-simple.c > > > > +++ b/drivers/gpu/drm/panel/panel-simple.c > > > > @@ -110,6 +110,7 @@ struct panel_simple { > > > > struct i2c_adapter *ddc; > > > > > > > > struct gpio_desc *enable_gpio; > > > > + struct gpio_desc *reset_gpio; > > > > > > > > struct drm_display_mode override_mode; > > > > }; > > > > @@ -433,12 +434,21 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc) > > > > if (IS_ERR(panel->supply)) > > > > return PTR_ERR(panel->supply); > > > > > > > > + panel->reset_gpio = devm_gpiod_get_optional(dev, "reset", > > > > + GPIOD_OUT_LOW); > > > > + if (IS_ERR(panel->reset_gpio)) { > > > > + err = PTR_ERR(panel->reset_gpio); > > > > + if (err != -EPROBE_DEFER) > > > > + dev_err(dev, "failed to request reset pin: %d\n", err); > > > > + return err; > > > > + } > > > > + > > > > > > However, I'm wondering if it wouldn't be better to just have the > > > device maintained in reset at probe (so OUT_HIGH) and moved out of > > > reset during either the prepare or enable callbacks. > > > > > > This is pretty much what is happening with the enable-gpios already. > > > > > > Also, panels usually need to wait for a minimum time after you > > > deassert the reset line. How is that dealt with? > > > > > > I guess a good way to do that would be to add that duration to the > > > panel description, since this is pretty much device specific. > > > > What about the case were your Bootloader displays something and you > > don't want the panel to blink ? > > The Bootloader to Linux transition will make the panel blink already, > since the display engine is going to be reset / reconfigured during > the transition. > > The only way to implement this would be to implement properly the > reset callbacks in all you display drivers to recreate the DRM state > from the hardware state, and then you'll be able to just switch to the > new buffer. > > Only Intel does this at the time though, and that's way outside of the > scope of this patch... > > > Right now I am just forcing the reset to be deasserted. > > ... Especially since the very next line after your patch forces the > panel to be disabled. > Is the addition of the reset support (as proposed by Maxime) interesting from your point of view? As you answered that you were not understanding the needs for such a change, I prefer to ask before spending more time on it. Thanks, Miquèl