From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="n5gk1bPg" Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6D48AF; Sat, 18 Nov 2023 09:33:10 -0800 (PST) Received: from pendragon.ideasonboard.com (213-243-189-158.bb.dnainternet.fi [213.243.189.158]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 62582DA7; Sat, 18 Nov 2023 18:32:40 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1700328760; bh=kYa/kdM1taEQ7R/xrgVMx238iKq4e7XT2QN4efJ7Pw0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=n5gk1bPgAXxXcGPwtOWmko/KRyVpTV8QszmV26oolOONf8kn6jP3sXdThpXYcma14 LiLqE/pYChNovqNzRgVb4+OaWinFuAXmBoFuOiMpBYZ/KAltbo8RqpTIjBRmNkAzz9 nUyoINyKslwV2OUCG8/Z4OxNOLm7OlepXilhW8tI= Date: Sat, 18 Nov 2023 19:33:15 +0200 From: Laurent Pinchart To: Sakari Ailus Cc: Jacopo Mondi , linux-acpi@vger.kernel.org, linux-media@vger.kernel.org, rafael@kernel.org Subject: Re: [PATCH v2 5/7] media: ov8858: Use pm_runtime_get_if_active(), put usage_count correctly Message-ID: <20231118173315.GD20846@pendragon.ideasonboard.com> References: <20231117111433.1561669-1-sakari.ailus@linux.intel.com> <20231117111433.1561669-6-sakari.ailus@linux.intel.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Hi Sakari On Sat, Nov 18, 2023 at 11:12:41AM +0000, Sakari Ailus wrote: > On Fri, Nov 17, 2023 at 04:30:15PM +0100, Jacopo Mondi wrote: > > On Fri, Nov 17, 2023 at 01:14:31PM +0200, Sakari Ailus wrote: > > > Use pm_runtime_get_if_active() to get the device's runtime PM usage_count > > > and set controls, then use runtime PM autosuspend once the controls have > > > been set (instead of likely transitioning to suspended state immediately). > > > > > > Signed-off-by: Sakari Ailus > > > --- > > > drivers/media/i2c/ov8858.c | 8 +++++--- > > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/media/i2c/ov8858.c b/drivers/media/i2c/ov8858.c > > > index 3af6125a2eee..a99b91700a8d 100644 > > > --- a/drivers/media/i2c/ov8858.c > > > +++ b/drivers/media/i2c/ov8858.c > > > @@ -1538,7 +1538,7 @@ static int ov8858_set_ctrl(struct v4l2_ctrl *ctrl) > > > struct v4l2_subdev_state *state; > > > u16 digi_gain; > > > s64 max_exp; > > > - int ret; > > > + int ret, pm_status; > > > > > > /* > > > * The control handler and the subdev state use the same mutex and the > > > @@ -1561,7 +1561,8 @@ static int ov8858_set_ctrl(struct v4l2_ctrl *ctrl) > > > break; > > > } > > > > > > - if (!pm_runtime_get_if_in_use(&client->dev)) > > > + pm_status = pm_runtime_get_if_active(&client->dev); > > > + if (!pm_status) > > > return 0; > > > > > > switch (ctrl->id) { > > > @@ -1601,7 +1602,8 @@ static int ov8858_set_ctrl(struct v4l2_ctrl *ctrl) > > > break; > > > } > > > > > > - pm_runtime_put(&client->dev); > > > + if (pm_status > 0) > > > > I'm not 100% sure I get this bit. > > > > If we get here it means pm_status is either -EINVAL or > 0, otherwise > > we would have exited earlier. > > > > What's the point of checking for > 0 here ? > > > > There are two cases where pm_status is -EINVAL, either !CONFIG_PM and > > the the below call is a nop, or if pm_runtime has not been enabled by > > the driver, which means the driver doesn't use pm_runtime at all. > > > > Are there other cases I have missed that require checking here for > > pm_status > 0 ? > > Other than Runtime PM being disabled, I don't think that should happen. > > So as such this patch does not fix a bug. I just prefer to be extra > cautious when it comes to use counts. What happened to the old motto of "if it's not broken, don't fix it" ? :-) I like how this series (slightly) simplifies the runtime PM API by giving pm_runtime_get_if_active() the right behaviour for the most common use cases. Let's continue in that direction, and evolve the API to simplify driver, not render them more complex. I would prefer refactoring this series to first switch drivers to pm_runtime_get_if_active(), and then use autosuspend at the end of the .s_ctrl() handler. That can be two patches, each modifying all relevant sensor driver. > > > + pm_runtime_mark_busy_autosusp(&client->dev); > > > > > > return ret; > > > } -- Regards, Laurent Pinchart