Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934497AbdCVMeu (ORCPT ); Wed, 22 Mar 2017 08:34:50 -0400 Received: from mail-io0-f193.google.com ([209.85.223.193]:35378 "EHLO mail-io0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759284AbdCVMeY (ORCPT ); Wed, 22 Mar 2017 08:34:24 -0400 MIME-Version: 1.0 In-Reply-To: <1490179594.2285.33.camel@pengutronix.de> References: <20161122134123.1209-1-peter.ujfalusi@ti.com> <20161122134123.1209-2-peter.ujfalusi@ti.com> <1490179594.2285.33.camel@pengutronix.de> From: Geert Uytterhoeven Date: Wed, 22 Mar 2017 13:30:32 +0100 X-Google-Sender-Auth: xTn7evj0e4a7HhCTsPtch3WO0M8 Message-ID: Subject: Re: [PATCH v4 1/2] backlight: pwm_bl: Move the checks for initial power state to a separate function To: Philipp Zabel Cc: Peter Ujfalusi , Lee Jones , Thierry Reding , Tomi Valkeinen , Linux PWM List , Linux Fbdev development list , "linux-kernel@vger.kernel.org" , Linus Walleij , "linux-gpio@vger.kernel.org" , Linux-Renesas Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4579 Lines: 105 Hi Philip, On Wed, Mar 22, 2017 at 11:46 AM, Philipp Zabel wrote: > On Tue, 2017-03-21 at 19:48 +0100, Geert Uytterhoeven wrote: >> On Tue, Nov 22, 2016 at 2:41 PM, Peter Ujfalusi wrote: >> > Move the checks to select the initial state for the backlight to a new >> > function and document the checks we are doing. >> >> This is far from a simple "move"... >> >> > With the separate function it is going to be easier to fix or improve the >> > initial power state configuration later and it is easier to read the code. >> > >> > Signed-off-by: Peter Ujfalusi >> > Reviewed-by: Philipp Zabel >> > Reviewed-by: Thierry Reding >> >> This patch (commit 7613c922315e308a in v4.11-rc1) broke the display on >> r8a7740/armadillo. >> >> > @@ -267,20 +292,16 @@ static int pwm_backlight_probe(struct platform_device *pdev) >> > pb->enable_gpio = gpio_to_desc(data->enable_gpio); >> > } >> > >> > - if (pb->enable_gpio) { >> > - /* >> > - * If the driver is probed from the device tree and there is a >> > - * phandle link pointing to the backlight node, it is safe to >> > - * assume that another driver will enable the backlight at the >> > - * appropriate time. Therefore, if it is disabled, keep it so. >> > - */ >> > - if (node && node->phandle && >> > - gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT && >> > - gpiod_get_value(pb->enable_gpio) == 0) >> > - initial_blank = FB_BLANK_POWERDOWN; >> > - else >> > - gpiod_direction_output(pb->enable_gpio, 1); >> >> In my case, "node" points to the "/backlight" node, but phandle is NULL. >> Hence before, gpiod_direction_output() was called to enable the GPIO... >> >> > - } >> > + /* >> > + * If the GPIO is configured as input, change the direction to output >> > + * and set the GPIO as active. >> > + * Do not force the GPIO to active when it was already output as it >> > + * could cause backlight flickering or we would enable the backlight too >> > + * early. Leave the decision of the initial backlight state for later. >> > + */ >> > + if (pb->enable_gpio && >> > + gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN) >> > + gpiod_direction_output(pb->enable_gpio, 1); >> >> ... while now it's no longer called, as gpiod_get_direction() returns >> -EINVAL. >> >> Indeed, r8a7740_pfc does not implement the .get_direction() callback, >> so gpiod_get_direction() always returns -EINVAL, which is never equal >> to GPIOF_DIR_IN. > > Oh, I didn't think about this at all, anymore. Though I believe to > remember that this was the reason that I checked for > (gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT) before, so ... > >> Restoring the old behavior by changing the above test to >> >> if (pb->enable_gpio && >> (!node || !node->phandle || >> gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN)) >> >> fixes the display for me, but leads to a more complex expression. >> >> However, changing the test to >> >> if (pb->enable_gpio && >> gpiod_get_direction(pb->enable_gpio) != GPIOF_DIR_OUT) >> >> also fixes the display, as an error is always different from GPIOF_DIR_OUT. >> >> Anyone with comments or suggestions to fix this for real? > > ... I'm in favor of the latter, as this is closer to the initial > intention. I'd also mention this in the comment: > > /* > * If the GPIO is not known to be already configured as output, that is, > * if gpiod_get_direction returns either GPIOF_DIR_IN or -EINVAL, change > * the direction to output and set the GPIO as active. > * Do not force the GPIO to active when it was already output as it > * could cause backlight flickering or we would enable the backlight too > * early. Leave the decision of the initial backlight state for later. > */ Thanks, I'll cook up a patch. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds