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 3AB7D1A23B7; Thu, 22 May 2025 05:47:18 +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=1747892839; cv=none; b=HmLdlzw6KFlHy+TVAizcSM1dVjunXf78UjxsdU0btius3J5cdSqCaW2HWxHGm9Yt3PdLc8/jUzrcj6WVpm4tpO3yDSemeZA34iC5IOgfl7a7fwwfVZwW2/JGjyCrxx3dvqjmtxMoABCxOv9YC+ANqdNGLMkyDkcSyVvCbl9aHLo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747892839; c=relaxed/simple; bh=OvBJFUTeD1fn/6i4rvUVGu2s79IT+JY7hcjKDidl78k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qxQ45a2yfzwimtRy20vI+B+fN0wmxo/9sAY/vR+DAA4VdOEegA8ww6jeeD3IIribcVCJuF/n3KMTTZlUVeELmyzlwN0nDVDNlml1Djn8O/yF+NCfmOlQD4PLOGkX9PDLt5W0/ek9cyAsrb3Kp4mpCx3S5nRT/0Jl/xB/N+gH+HQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gRgC3Pub; 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="gRgC3Pub" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3FFA1C4CEE4; Thu, 22 May 2025 05:47:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747892838; bh=OvBJFUTeD1fn/6i4rvUVGu2s79IT+JY7hcjKDidl78k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gRgC3PubJEkYoFhk5/eL7JHJQ7kcr4piLda2/KZE0wC5u1GNbNXOoDfNDuP4CJexB nrsA1uFHr6s2dcPyL6CBqxCTJgXdk7hav/FK/rGg9ZL9SkYeJf1tOTHKSvNqYLAVUN U1IJgMakr4Qxbgu/PNI17xVgbTjs3OqT8/Br+Hlfn3opp6WAbpeYuL+XVkniVak8ei mscrNq+ENG1imDXTLG3yZ8Gg42u+BTY2JPZFivWAM3tlXNIWc3Wm1xnTLq5wdfSyMA AmZg7qnEER1Q2Y4vazlDBDD70HSLraOFa2TSzgSFyAWbYJ8cAmvJ6d9pgBPh2+QkVB vCyb5oPO/sdWw== Date: Thu, 22 May 2025 07:47:12 +0200 From: Danilo Krummrich To: Greg Kroah-Hartman Cc: Remo Senekowitsch , Rob Herring , Saravana Kannan , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , "Rafael J. Wysocki" , Dirk Behme , linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH v5 4/9] rust: device: Enable printing fwnode name and path Message-ID: References: <20250520200024.268655-1-remo@buenzli.dev> <20250520200024.268655-5-remo@buenzli.dev> <2025052153-steadier-bargraph-e81a@gregkh> <2025052116-gem-blend-2585@gregkh> <2025052244-untaken-spied-868b@gregkh> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2025052244-untaken-spied-868b@gregkh> On Thu, May 22, 2025 at 06:49:15AM +0200, Greg Kroah-Hartman wrote: > On Wed, May 21, 2025 at 09:13:08PM +0200, Danilo Krummrich wrote: > > On Wed, May 21, 2025 at 08:36:10PM +0200, Remo Senekowitsch wrote: > > > On Wed May 21, 2025 at 6:58 PM CEST, Greg Kroah-Hartman wrote: > > > > On Wed, May 21, 2025 at 03:03:07PM +0200, Remo Senekowitsch wrote: > > > >> On Wed May 21, 2025 at 2:02 PM CEST, Greg Kroah-Hartman wrote: > > > >> > On Tue, May 20, 2025 at 10:00:19PM +0200, Remo Senekowitsch wrote: > > > >> >> Add two new public methods `display_name` and `display_path` to > > > >> >> `FwNode`. They can be used by driver authors for logging purposes. In > > > >> >> addition, they will be used by core property abstractions for automatic > > > >> >> logging, for example when a driver attempts to read a required but > > > >> >> missing property. > > > >> >> > > > >> >> Signed-off-by: Remo Senekowitsch > > > >> >> --- > > > >> >> rust/kernel/device/property.rs | 72 ++++++++++++++++++++++++++++++++++ > > > >> >> 1 file changed, 72 insertions(+) > > > >> >> > > > >> >> diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs > > > >> >> index 70593343bd811..6ccc7947f9c31 100644 > > > >> >> --- a/rust/kernel/device/property.rs > > > >> >> +++ b/rust/kernel/device/property.rs > > > >> >> @@ -32,6 +32,78 @@ pub(crate) fn as_raw(&self) -> *mut bindings::fwnode_handle { > > > >> >> self.0.get() > > > >> >> } > > > >> >> > > > >> >> + /// Returns an object that implements [`Display`](core::fmt::Display) for > > > >> >> + /// printing the name of a node. > > > >> >> + pub fn display_name(&self) -> impl core::fmt::Display + '_ { > > > >> >> + struct FwNodeDisplayName<'a>(&'a FwNode); > > > >> >> + > > > >> >> + impl core::fmt::Display for FwNodeDisplayName<'_> { > > > >> >> + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { > > > >> >> + // SAFETY: self is valid by its type invariant > > > >> >> + let name = unsafe { bindings::fwnode_get_name(self.0.as_raw()) }; > > > >> >> + if name.is_null() { > > > >> >> + return Ok(()); > > > >> > > > > >> > So if there is no name, you are returning Ok()? Are you sure that's ok > > > >> > to do? What will the result of the string look like then? > > > >> > > > >> In that case we're not writing anything to the formatter, which is > > > >> equivalent to an empty string. `Ok(())` means that writing succeeded. > > > >> > > > >> I assumed that a valid node would always have a name. And we're > > > >> guaranteed to have a valid node. So I assumed this case would never > > > >> happen and didn't think too hard about it. But even if a valid node has > > > >> not name, empty string is probably the correct thing, right? > > > > > > > > I don't know what this "name" is used for. An empty string might not be > > > > what you want to use here, given that you could be naming something > > > > based on it, right? fwnode_get_name() is used for many things, > > > > including the detection if a name is not present at all, and if not, > > > > then the code needs to clean up and abort. > > > > > > > > So what exactly are you going to be using this for? > > > > > > Valid question... I'm not using it for anything. > > > > You're using this in PropertyGuard::required_by(), where you use display_path() > > and hence display_name() to print the node path in the error case. > > > > So, currently, this is only used in the error case when a property of a given > > node that is required by a driver can't be found. > > And in that case, the "normal" dev_err() output should be all that is > needed here, not a "pretty printer" that might fail to document it at > all :) That's what the code does; PropertyGuard::required_by() uses dev_err!() to print the string. It's just that the functions from the C side that provide the strings are abstracted in an implementation of core::fmt::Display for the FwNode, which is the idiomatic way to abstract a string representations of a type. And since Display::fmt() is fallible, we need to decide if NULL is a valid value for fwnode_get_name() to return. The interface, i.e. struct fwnode_operations, does not document this, but to me it seems that fwnode_get_name() returning a NULL pointer is an error case.