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 5F04E6EB56; Fri, 28 Jun 2024 19:08:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719601722; cv=none; b=iq6qjFRu5PeFaxjkXnqhWp/nKORmN43xsfRdCSR6yC+18mF0PplorJOesrU6kwAiPOi+chSebYkZ9DNbyMIXQ/8UWfLx3+3nQ/Niopgos8n3adMNY9aFYYZ9AFgdwiJ350Z4BkRhefECb7iEmR9Gj6n82qOsTc9ZzCgy57ZUcq0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719601722; c=relaxed/simple; bh=e9grNQ3HIDWrOxb68W815q7PLDeOfmbqGLJtbuYESHM=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Ux5SICgBpWphvr7dTEMdVDLwN5EoyneATboZzkKVCrCEqv2xv4FFT2RNgHPZCwBn1iuabWlDV39AAKikw4ijBthlPriMIV4NYrtFFbKdJD0xS/p4OJsjZwV73Cq3+SK8GQblDp055kpFwpOQ+83xyX/xlnVc0ayj8LfnLQlgwt8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qknRx32z; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qknRx32z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D31B3C116B1; Fri, 28 Jun 2024 19:08:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719601721; bh=e9grNQ3HIDWrOxb68W815q7PLDeOfmbqGLJtbuYESHM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=qknRx32z/f0BEsD7wRERvSvK05nFQ9raDozdkbS08y2foJ+3Nbpi0j5nQytQB90D/ 0VF+J9qYuM/29Hee7ASc9PtH4oZAPRq+nyHhIuHu+jaYxApdgJiCRKQXL63lqVqTK3 K8X1XKq3QUFmhfNbLCaPnqqB6YwuwDHkT5uF6DAK8/tzM4kP5Yp2mQPf7nR2SJ5Dr2 S8DKosUq6f5yW1UfLT5JXynB0VEAgLWnxDDrh1tq4oA+jiuO3suHgbf2dJYjajrrA4 LcAPvQkVJJSOli2Mp6wDpSUG/5IdzR0I0pCcRDCExWUSl9i56uG5diY6+IgXovZwNN g45LJagz6AboQ== Date: Fri, 28 Jun 2024 20:08:34 +0100 From: Jonathan Cameron To: Sean Anderson Cc: Guenter Roeck , Jean Delvare , linux-iio@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, Lars-Peter Clausen Subject: Re: [PATCH v2 2/2] hwmon: iio: Add labels from IIO channels Message-ID: <20240628200834.44c6453a@jic23-huawei> In-Reply-To: References: <20240624174601.1527244-1-sean.anderson@linux.dev> <20240624174601.1527244-3-sean.anderson@linux.dev> <20240624202433.29564802@jic23-huawei> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 27 Jun 2024 14:37:01 -0400 Sean Anderson wrote: > On 6/24/24 15:24, Jonathan Cameron wrote: > > On Mon, 24 Jun 2024 11:47:39 -0700 > > Guenter Roeck wrote: > > > >> On 6/24/24 10:46, Sean Anderson wrote: > >> > Add labels from IIO channels to our channels. This allows userspace to > >> > display more meaningful names instead of "in0" or "temp5". > >> > > >> > Although lm-sensors gracefully handles errors when reading channel > >> > labels, the ABI says the label attribute > >> > > >> >> Should only be created if the driver has hints about what this voltage > >> >> channel is being used for, and user-space doesn't. > >> > > >> > Therefore, we test to see if the channel has a label before > >> > creating the attribute. > >> > > >> > >> FWIW, complaining about an ABI really does not belong into a commit > >> message. Maybe you and lm-sensors don't care about error returns when > >> reading a label, but there are other userspace applications which may > >> expect drivers to follow the ABI. Last time I checked, the basic rule > >> was still "Don't break userspace", and that doesn't mean "it's ok to > >> violate / break an ABI as long as no one notices". > >> > >> > Signed-off-by: Sean Anderson > >> > --- > >> > > >> > Changes in v2: > >> > - Check if the label exists before creating the attribute > >> > > >> > drivers/hwmon/iio_hwmon.c | 45 ++++++++++++++++++++++++++++++++++----- > >> > 1 file changed, 40 insertions(+), 5 deletions(-) > >> > > >> > diff --git a/drivers/hwmon/iio_hwmon.c b/drivers/hwmon/iio_hwmon.c > >> > index 4c8a80847891..5722cb9d81f9 100644 > >> > --- a/drivers/hwmon/iio_hwmon.c > >> > +++ b/drivers/hwmon/iio_hwmon.c > >> > @@ -33,6 +33,17 @@ struct iio_hwmon_state { > >> > struct attribute **attrs; > >> > }; > >> > > >> > +static ssize_t iio_hwmon_read_label(struct device *dev, > >> > + struct device_attribute *attr, > >> > + char *buf) > >> > +{ > >> > + struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr); > >> > + struct iio_hwmon_state *state = dev_get_drvdata(dev); > >> > + struct iio_channel *chan = &state->channels[sattr->index]; > >> > + > >> > + return iio_read_channel_label(chan, buf); > >> > +} > >> > + > >> > >> I personally find it a bit kludgy that an in-kernel API would do a > >> sysfs write like this and expect a page-aligned buffer as parameter, > >> but since Jonathan is fine with it: > > > > That's a good point that I'd not picked up on and it probably makes sense > > to address that before it bites us on some other subsystem. > > > > It was more reasonable when the only path was to a light wrapper that went > > directly around the sysfs callback. Now we are wrapping these up for more > > general use we should avoid that restriction. > > > > Two approaches to that occur to me. > > 1) Fix up read_label() everywhere to not use sysfs_emit and take a size > > of the buffer to print into. There are only 11 implementations so > > far so this should be straight forward. > > This API is the same as the existing iio_read_channel_ext_info. It is > used for the same purpose: forwarding sysfs reads/writes from one > device to another (see e.g. iio-mux and iio-rescale). ext_info is used > by around 85 drivers, so it is not so trivial to change the API. While I > agree that the current API is unusual, it's not too bad given that we > get the same guarantees from device_attribute.show. Fair enough. Maybe we can clean this up at somepoint but let's not do it today. Applied to the togreg branch of iio.git and pushed out as testing for 0-day to poke at it and maybe find something we missed. Jonathan > > --Sean > > > 2) Add a bounce buffer so we emit into a suitable size for sysfs_emit() > > then reprint from there into a buffer provided via this interface with > > the appropriate size provided. This one is clunky and given the relatively > > few call sits I think fixing it via option 1 is the better route forwards. > >