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[46.193.119.166]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4601f2dcad5sm68854439f8f.5.2026.06.09.08.03.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Jun 2026 08:03:32 -0700 (PDT) Message-ID: <49c78c6e-5ccd-4789-ae53-359d4e5794c8@gmail.com> Date: Tue, 9 Jun 2026 17:03:21 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v9 2/3] net: ethtool: add KSZ87xx low-loss cable PHY tunables To: Jakub Kicinski , Marek Vasut Cc: Paolo Abeni , woojung.huh@microchip.com, UNGLinuxDriver@microchip.com, andrew@lunn.ch, olteanv@gmail.com, davem@davemloft.net, edumazet@google.com, maxime.chevallier@bootlin.com, horms@kernel.org, hkallweit1@gmail.com, linux@armlinux.org.uk, Tristram.Ha@microchip.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, nb@tipi-net.de, fidelio.lawson@exotec.com References: <20260601-ksz87xx_errata_low_loss_connections-v9-2-fdbbb15592cb@exotec.com> <20260604114119.170747-1-pabeni@redhat.com> <20260604193545.0a906598@kernel.org> <4098dafb-838e-4854-add6-cb3ce6668a70@nabladev.com> <20260605163142.4bbcf502@kernel.org> Content-Language: en-US From: Fidelio LAWSON In-Reply-To: <20260605163142.4bbcf502@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/6/26 01:31, Jakub Kicinski wrote: > On Fri, 5 Jun 2026 05:16:54 +0200 Marek Vasut wrote: >> On 6/5/26 4:35 AM, Jakub Kicinski wrote: >>> On Thu, 4 Jun 2026 13:41:19 +0200 Paolo Abeni wrote: >>>> [Severity: High] >>>> Is it intentional to enforce an 8-bit type constraint for bandwidth and DSP >>>> equalizer tunables? >>>> >>>> This heavily couples the global API to the 8-bit register layout of the >>>> KSZ87xx hardware without defining generic units like Hz for bandwidth. >>> >>> AFAIK this is the one comment from AI that survives scrutiny. >>> Seems unlikely we'd need more bits, but then again - why not. >>> u32 should be our default for integer values, u8 is more for >>> booleans. >> >> Why waste memory space if we are already sure the space would not be used. > > Waste what memory? We are talking about a syscall argument effectively. > > My point is that this is adding the arguments as u8 in > net/ethtool/ioctl.c, so as part of the global uAPI. > > The driver can still store these as u8, since any value outside of that > range is invalid for ksz87xx, and the input is properly validated. > But we shouldn't constrain the value "in transit", at the uAPI level. > Another driver may need a larger range (however unlikely that is). Thanks for the clarification. I will update the series to use u32 for the PHY tunables in the next revision, while keeping the driver-side representation constrained to the supported range. Thanks, Fidelio