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[217.229.17.248]) by smtp.gmail.com with ESMTPSA id a27sm2656581eda.65.2018.11.14.04.47.53 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 14 Nov 2018 04:47:53 -0800 (PST) Date: Wed, 14 Nov 2018 13:47:52 +0100 From: Thierry Reding To: Ryder Lee Cc: Rob Herring , linux-pwm@vger.kernel.org, Weijie Gao , Roy Luo , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, John Crispin Subject: Re: [resend PATCH 1/3] pwm: mediatek: drop flag 'has_clks' Message-ID: <20181114124752.GI2620@ulmo> References: <4c9044427b1aab373acd6ac76f0c905e2be79784.1542074855.git.ryder.lee@mediatek.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="KrHCbChajFcK0yQE" Content-Disposition: inline In-Reply-To: <4c9044427b1aab373acd6ac76f0c905e2be79784.1542074855.git.ryder.lee@mediatek.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --KrHCbChajFcK0yQE Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Nov 13, 2018 at 10:08:22AM +0800, Ryder Lee wrote: > The flag 'has_clks' and related checks are superfluous as the CCF > subsystem does this for you. Both of these mechanisms aren't equivalent. While CCF can deal with optional clocks, what the has_clks flag actually means is that the device doesn't need a clock (or doesn't have a clock input) on the devices where it is cleared. So I'd actually be in favor of keeping the has_clks property because it serves as an additional sanity check. For example if you run this driver on an SoC that "has clocks" but if you don't list them in DT, then after this patch the driver will happily continue without clocks, even though it may break completely without those clocks. I've seen SoCs respond to disabled clocks for a hardware block in different ways, in many cases an access to any of the registers will completely hang the CPU. In other cases it may just crash in some other way or give you some sort of machine exception. None of those are good, and make the tiny bit of additional code required to support the has_clks flag very attractive. But that's just my opinion. If you prefer to throw away that safety barrier, be my guest. But if you do, please move this functionality into the clock framework first and then make the driver use it. Thierry --KrHCbChajFcK0yQE Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEiOrDCAFJzPfAjcif3SOs138+s6EFAlvsGXUACgkQ3SOs138+ s6EhKhAAnU52kPmOfIbVhaDxXLLAR5p0eNkpLB7VYzDDiizJGgdGfnpjgjwqPHb0 6pJf12Bo+bibjOzR/kHwv6du6ylwESC73/ZyZnFlrvGJkF2CVXgJny5vfbBxPb9X VsRkrRjCNK4Gi4jSOieGGH3k6BpUc/xnWzlF4wkSMTl7ualJ09gct2YgrnQSgvD5 Ku1CsxGsHACXWi78uPUEjavXSkeHFHwevpRzkekeAQCzNZe12kSHbPmnHUI6lXQo XcXvKvD6pPwPHXnMV40pKi8kldWhT6CBX/1MgukimbkxDMtUbhCLhOT1WIxn4DW8 lM1MndqkdF/CzHpop/eMQS0OTOaFI5/6NlROEjz8dOG0/RKrkgH0CxnjgeCIaDqI jmNf0/iEVSyqsA7RbNiz4AneOfNLMlkhTTdRDU+XZukWiOKqCgStQHqfUsbeRcyV L/ERoC/y33co9MAVYs+NVawNLu+a1344Z58d3BIR7GNO6P+DtV6W9Z5eC03rW+MP swVsPUkMZZblcM2oE3nFEa3OoTO82aIIfrjqC13mx5iHTa6/USWRlBIwXqEZgpd+ 6gOEk3pdlR5QMRgs0ijBL85IR0PWusV2SX0eZk9ndCX2abRaBA88ZJbZacBeIilZ 9KYjAopAuEg6RKeweYL93hYktnxvJJ+DLxzpaf9Lz1HheOn52nQ= =dqiR -----END PGP SIGNATURE----- --KrHCbChajFcK0yQE--