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Wed, 11 Oct 2023 06:19:38 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-1019-ged83ad8595-fm-20231002.001-ged83ad85 MIME-Version: 1.0 Message-Id: In-Reply-To: <2023101126-stash-manor-7162@gregkh> References: <20231010224928.2296997-1-peter.griffin@linaro.org> <20231010224928.2296997-9-peter.griffin@linaro.org> <2023101111-banknote-satin-1f77@gregkh> <2023101137-fester-rerun-5c39@gregkh> <2023101126-stash-manor-7162@gregkh> Date: Wed, 11 Oct 2023 12:19:18 +0200 From: "Arnd Bergmann" To: "Greg Kroah-Hartman" Cc: "Tudor Ambarus" , "Peter Griffin" , "Rob Herring" , krzysztof.kozlowski+dt@linaro.org, "Michael Turquette" , "Conor Dooley" , "Stephen Boyd" , "Tomasz Figa" , "Sylwester Nawrocki" , "Linus Walleij" , "Wim Van Sebroeck" , "Guenter Roeck" , "Catalin Marinas" , "Will Deacon" , "Olof Johansson" , "Chanwoo Choi" , andre.draszik@linaro.org, semen.protsenko@linaro.org, saravanak@google.com, "William McVicker" , soc@kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-clk@vger.kernel.org, "open list:GPIO SUBSYSTEM" , linux-watchdog@vger.kernel.org, kernel-team@android.com, linux-serial@vger.kernel.org Subject: Re: [PATCH v2 08/20] dt-bindings: serial: samsung: Add google-gs101-uart compatible Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Wed, Oct 11, 2023, at 11:42, Greg Kroah-Hartman wrote: > On Wed, Oct 11, 2023 at 11:30:25AM +0200, Arnd Bergmann wrote: >> On Wed, Oct 11, 2023, at 10:57, Greg KH wrote: >> > >> >> It's not only the IP itself >> >> that can differ, it's also the integration of the IP into the final >> >> product that could have an influence on the behavior. >> > >> > This is for the Pixel 6, a device that is no longer even shipping. The >> > "final product" is long stable, so this should not be an issue. >> >> The driver does have soc specific settings for each compatible >> string, in this case it looks like it overrides the FIFO size >> based on driver specific data and the order in which the >> ports are probed [1]. I don't understand why the driver does >> this, but my impression is that if we wanted to change it to no >> longer rely on that data, we'd also need a new compatible >> string. > > As I reviewed that patch already, it is just duplicating an existing > quirk/device that the driver already supports, so there is no need for > any "new device type" to be added to that driver, just use the existing > hardware description in the dt and all should be fine. The thing is, I suspect that the FIFO size override is actually wrong for the exynos850 as well, and is almost certainly wrong for both exynosautov9 and google-gs101: - The driver overrides an exynos850 compatible uart to use a 256 byte FIFO on whichever port is probed first, 64 byte on the next three ports, and the setting from DT on any later ones, falling back to 16 bytes if the DT does not set anything. - exynos850 only actually has three of these ports, not four. It does not lists FIFO size in the dts at all. - exynosautov9 has a total of 11 ports, each of these compatible with both "samsung,exynosautov9-uart" as the specific value and "samsung,exynos850-uart" as the generic fallback. The DT lists a FIFO size of 256 bytes for ports 0, 1, and 6, but lists FIFO size 64 for each of the other ones. - google-gs101 only lists a single uart in the dts, and sets it to a 256 byte FIFO. - testla-fsd claims to be compatible with exynos4210, which also overrides the first two ports in probe order to 256 and 64 bytes respectively (like exynos850), but it only has two ports. - artpec8 has a separate compatible string so it overrides all ports to 64 bytes. I don't know why probe order would have anything to do with this, so most likely these are all the same thing and should just put a fixed FIFO size into the DT for each port instance. Arnd