From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3AEA920E3 for ; Thu, 13 Oct 2022 05:49:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDDDCC433C1; Thu, 13 Oct 2022 05:49:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1665640192; bh=3fyap5LhSza2L+4JHuJ6ML5HQdF9DEP7yZF+q8oMha8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PyQeKUdorM33zBwvzzNEUPgVBlmD2cDNcA7+SGKG2KEwXmLfzjMxK3Z/ClCy9eSmC 9OkKwOOTLxCCq/YJOqPu3bk60BkkixwJQleCpjlCTEfviv9UTwm48OG3TMXYlh3QAI IFFHWdwbXHfbisPzsXCufu3m1+sfw9dYdDITzAnagZ/oq6f/hL8UDQUbxzq43WUmgh CPKfI+hsnvxILmduWxaJIiyvZ76Jj6hkmHg6NcMqHhiXIiqjg3rNE3Oyfl0typN80Z d6bChRUzjISnf7FnQi44gVp/7oTgyebM6iyHHU7phwbBxk8HvUzijSpyTEtlC+xbMJ J7rJXyICY3S0Q== Date: Thu, 13 Oct 2022 13:49:49 +0800 From: Tzung-Bi Shih To: Dan Callaghan Cc: chrome-platform@lists.linux.dev, LKML , Sami =?iso-8859-1?Q?Ky=F6stil=E4?= , Benson Leung Subject: Re: [PATCH v5 1/1] platform/chrome: add a driver for HPS Message-ID: References: <20221012040918.272582-1-dcallagh@chromium.org> <20221012040918.272582-2-dcallagh@chromium.org> Precedence: bulk X-Mailing-List: chrome-platform@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Oct 12, 2022 at 09:29:03PM -0700, Dan Callaghan wrote: > Excerpts from Tzung-Bi Shih’s message of 2022-10-12 19:46:51 +1100: > > On Wed, Oct 12, 2022 at 03:09:18PM +1100, Dan Callaghan wrote: > > > + hps->enable_gpio = devm_gpiod_get(&client->dev, "enable", GPIOD_OUT_HIGH); > > > + if (IS_ERR(hps->enable_gpio)) { > > > + ret = PTR_ERR(hps->enable_gpio); > > > + dev_err(&client->dev, "failed to get enable gpio: %d\n", ret); > > > + return ret; > > > + } > > > + > > > + ret = misc_register(&hps->misc_device); > > > + if (ret) { > > > + dev_err(&client->dev, "failed to initialize misc device: %d\n", ret); > > > + return ret; > > > + } > > > + > > > + hps_set_power(hps, false); > > > > IIUC, the GPIO will raise to HIGH in the first place, and then fall > > to LOW until here. Is it an expected behavior? How about gpiod_get() > > with GPIOD_OUT_LOW? > > It might seem a little unusual, but it is intentional. The enable line is > already high when we enter the kernel from firmware. Acquiring the GPIO > line with GPIOD_OUT_HIGH preserves its existing state (high) in case later > steps fail. > > We power off the periphal only once the driver is successfully bound and has > taken control of its power state. I see. Please put some context comments before calling devm_gpiod_get(). > > > +static int hps_i2c_remove(struct i2c_client *client) > > > +{ > > > + struct hps_drvdata *hps = i2c_get_clientdata(client); > > > + > > > + pm_runtime_disable(&client->dev); > > > + misc_deregister(&hps->misc_device); > > > + hps_set_power(hps, true); > > > > Why does it need to raise the GPIO again when removing the device? > > Similar to the above, we want to preserve the default power state > (i.e. powered on) whenever the driver is not bound to the device. > > This behaviour made sense to us mainly because we were originally controlling > the peripheral entirely from userspace, so it was always powered on by default. > > Do you think this behaviour is acceptable, or do we need to change it? I think it's fine. Please put some context comments before calling hps_set_power().