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([144.202.86.13]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b0db13a3e63sm1684024a12.29.2025.04.18.11.21.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Apr 2025 11:21:38 -0700 (PDT) From: Pengyu Luo To: daniel@riscstar.com Cc: conor+dt@kernel.org, danielt@kernel.org, deller@gmx.de, devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org, jingoohan1@gmail.com, krzk+dt@kernel.org, lee@kernel.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-leds@vger.kernel.org, lujianhua000@gmail.com, mitltlatltl@gmail.com, pavel@kernel.org, robh@kernel.org Subject: Re: [PATCH 2/4] backlight: ktz8866: add slave handler Date: Sat, 19 Apr 2025 02:19:09 +0800 Message-ID: <20250418181927.208018-1-mitltlatltl@gmail.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-leds@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, Apr 8, 2025 at 12:27 AM Daniel Thompson wrote: > On Mon, Apr 07, 2025 at 05:51:17PM +0800, Pengyu Luo wrote: > > Kinetic ktz8866, found in many android devices, nowadays, some oem use > > dual ktz8866 to support a larger panel and higher brightness, original > > driver would only handle half backlight region on these devices, > > registering it twice is unreasonable, so adding the slave handler to > > support it. > > Is there anything unique about KTZ8866 that allows it to be used like > this? I think it would be better to add support for secondary backlight > controllers into the backlight framework, rather than having to > implement driver specific hacks for every backlight controller that > appears in a primary/secondary configuration. > According to my understanding, if I add the new api to backlight framework, with a minimal modification, then I either do A or do B(I doubt it is my fixed mindset) A: Tied two devices, registering the primary and the secondary device during one probe, to do that, I access another KTZ8866 when probing. Those hack is still here, that doesn't seem to help. B: Uncoupled, probing separately, the later one is registered as the secondary one. Brightness control is a little uncoupled, there are two sysfs, I doubt if userspace programs will write brightness to two devices. Then we need synchronization, write primary => write primary and write secondary, viceversa. > Also, the kernel seeks to avoid adding new instances of master/slave > terminology. See the coding style doc for suggested alternatives: > https://www.kernel.org/doc/html/latest/process/coding-style.html#naming > Agree. Best wishes, Pengyu