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 025F63D6486; Mon, 27 Apr 2026 19:02:33 +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=1777316556; cv=none; b=WZfE5wryYui8KFCAtG2vkosyLtaGk0/FaYTlwSk/ljpklztArbymAWOlDXnDmecBYVqSkA3dy5lLHCUecKC70x8ijXJ/RFUYUaQJ0cd+zKHAy9Y/hZySxRH6Y2A3pbwWPLQSBOO46gUSnGgU2YHzssfrYqq/Mn21c1TjyalU3ZI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777316556; c=relaxed/simple; bh=QiOW0pRNHKjZQb0GCanC1NBjMtUFbjV5l/TrrAVmxWs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ULhoopjh+muDpIqr3QPdFSe4EuElvaahxHPT4dDLPTSkHimmViA++hmvjttHZh921W44lPja3W2h6Ilv2lQRObOQp2JE7zAUDOuXIWeF39kbi4avqjNLOpUBl4sfULkgDlXj5iejSePnyV8KlzcTAt9gpKULQShHU/Swa4s1dgA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ipzDKaxZ; 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="ipzDKaxZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 333DCC19425; Mon, 27 Apr 2026 19:02:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777316553; bh=QiOW0pRNHKjZQb0GCanC1NBjMtUFbjV5l/TrrAVmxWs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ipzDKaxZTuYcAn0cwLm7hq2XD+tz2MXHj3hQCRF6ub1hXDlCIYhssR2xm92TremKK O/qRkTwREQsWry8sV74JN5RCnXLRNr4JeghoNVLrRWjm6aLxotzbvmQ3v/tsh7VWhP ktrJsy9iRPx3UyRP5J3TdSLoEPEjJOt9bzM8r5eMhBY5zMKDHBhD1lFf0yleY/YHTu 05NKP7JCd+sQjg5kt5itL3MYDSzmGWmgof+C5Db+5StrwBxr+8IBqP+nl8FwfN4qS6 wu1NYpNpjul+Im+HFfD3zj9YbQt/F7/L+ufDX9t2CID8X2zjWwqqIMX6D0zT1PE1zt k7JsDI3/nHjhQ== Date: Mon, 27 Apr 2026 20:02:29 +0100 From: Conor Dooley To: Krzysztof Kozlowski Cc: Rob Herring , Krzysztof Kozlowski , Conor Dooley , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Conor Dooley Subject: Re: [PATCH v2] docs: dt: writing-bindings: Extend compatible fallbacks guideline Message-ID: <20260427-squishier-outclass-bb25f2f83dd1@spud> References: <20260427160739.175451-2-krzysztof.kozlowski@oss.qualcomm.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="Bx6+VBo+jgc1wxgT" Content-Disposition: inline In-Reply-To: <20260427160739.175451-2-krzysztof.kozlowski@oss.qualcomm.com> --Bx6+VBo+jgc1wxgT Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Apr 27, 2026 at 06:07:40PM +0200, Krzysztof Kozlowski wrote: > Extend the guidelines when to use fallback compatibles to cover to > common review responses. Devices are most likely compatible and should > use fallbacks when having: >=20 > 1. Compatible programming interface, meaning one is a subset, and Linux > device drivers can use the subset to correctly match/bind and still > operate with the subset features. >=20 > 2. Device variant discovery through some means, like registers. >=20 > Devices are incompatible and fallback is not suitable when that > fallback cannot be used by the drivers to match/bind. In the same time > commit message should clearly explain when the code suggests devices > are compatible, but the binding does not define them as such. >=20 > Acked-by: Conor Dooley > Signed-off-by: Krzysztof Kozlowski >=20 > --- >=20 > Changes in v2: > 1. Include Conor's suggestion about commit msg, a bit rephrased. Ye, it's better than my double use of the same term. > 2. Add tag > 3. Drop double-space, because file does not use that format (old habit). > --- > .../devicetree/bindings/writing-bindings.rst | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) >=20 > diff --git a/Documentation/devicetree/bindings/writing-bindings.rst b/Doc= umentation/devicetree/bindings/writing-bindings.rst > index 667816dd7d50..1a51764833a1 100644 > --- a/Documentation/devicetree/bindings/writing-bindings.rst > +++ b/Documentation/devicetree/bindings/writing-bindings.rst > @@ -53,7 +53,17 @@ Properties > - DON'T use wildcards or device-family names in compatible strings. > =20 > - DO use fallback compatibles when devices are the same as or a super= set of > - prior implementations. > + prior implementations. Fallback compatibles are applicable especial= ly > + when sharing a programming interface or when able to discover the > + variants. > + > + - DON'T add fake fallback compatibles when software cannot use such t= o match > + and bind to a device, and still operate correctly. > + > + - DO use the commit message to explain why devices that may appear > + compatible in a diff (e.g. no differences in property use, same han= dling > + by the software) but are not made compatible in the binding, are not > + compatible. > =20 > - DO add new compatibles in case there are new features or bugs. > =20 > --=20 > 2.51.0 >=20 --Bx6+VBo+jgc1wxgT Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRh246EGq/8RLhDjO14tDGHoIJi0gUCae+yxQAKCRB4tDGHoIJi 0qbhAQDfy8lQlSn6/HD1jVJZE0bmvAWinM/vTVsXO8NRK3ujEAEA7E/H7gqtBzUv yYEdndf1mc/a36YFZhlbf105Y974iwI= =pj18 -----END PGP SIGNATURE----- --Bx6+VBo+jgc1wxgT--