From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 0F8FB2139D6 for ; Thu, 27 Jun 2024 18:37:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719513434; cv=none; b=cQjnwGty+znafPTiH/l7+oB/FBQ0ya2hgGfbc068AMiqTA77piCowyMR5gXlmuMkGidBJ0VrUGEosTfUrh55N0ZpUKjjVfyT2NOtab7k/lXxeSnd/eD6HwlaWWQQg6qSWWVBq6dTA4/PzMtoxGteBhhdegBSktP77ozCpNnDg7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719513434; c=relaxed/simple; bh=kMf/jTaHv8Pibllz765oLhr56R7Vnv74xKa/hCJTaII=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=j9ji6Zl10t9Olr4g5q2nLxeTGF4inqLm0dpyf3mUxsTj6PSUZ/tCV6CJIGjc5qKzOGTZvTbgPLWsBYgafw6tE4fWCIO3Ju8ErwWbLcFYDiHc6oZka1OaIUnYGfsE08yaBHw7kudXExPCc2nqLvgsM7lxcrNGpA2vq88DKODLd8c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=W1534gzr; arc=none smtp.client-ip=95.215.58.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="W1534gzr" X-Envelope-To: jic23@kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1719513429; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LcX+DNUAOkuuXE8/JmszLDMKosfH1JHvU1xDYWp+oWM=; b=W1534gzrjEl4P8g5y/J0X5tfxFPrE1J+gIoykAKtFAUDacat2D3PUXImDN83E0bM/P+BpT K7ISNAsIhoBPqPifciJwK9EXKDrrvbGq+eKB6x1s5dPhSqU39VJu3aKZ/qnhjExFyVhT6C SSZPLqZK48b82/3359XmIQkrvpwND4Y= X-Envelope-To: linux@roeck-us.net X-Envelope-To: jdelvare@suse.com X-Envelope-To: linux-iio@vger.kernel.org X-Envelope-To: linux-hwmon@vger.kernel.org X-Envelope-To: linux-kernel@vger.kernel.org X-Envelope-To: lars@metafoo.de Message-ID: Date: Thu, 27 Jun 2024 14:37:01 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2 2/2] hwmon: iio: Add labels from IIO channels To: Jonathan Cameron , Guenter Roeck Cc: Jean Delvare , linux-iio@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, Lars-Peter Clausen References: <20240624174601.1527244-1-sean.anderson@linux.dev> <20240624174601.1527244-3-sean.anderson@linux.dev> <20240624202433.29564802@jic23-huawei> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Sean Anderson In-Reply-To: <20240624202433.29564802@jic23-huawei> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT 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. --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.