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Tue, 22 Sep 2026 05:12:45 -0700 (PDT) Received: from cachyos-aura ([45.112.148.109]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-144f29d8762sm5091159c88.5.2026.09.22.05.12.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 05:12:44 -0700 (PDT) From: Navon John Lukose To: Mika Westerberg Cc: Andy Shevchenko , Andi Shyti , linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] i2c: designware: size the RX FIFO threshold to the queued transfer Date: Tue, 22 Sep 2026 17:42:38 +0530 Message-ID: <20260922121238.46016-1-navonjohnlukose@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260922065041.GC106095@black.igk.intel.com> References: <20260919232647.448748-1-navonjohnlukose@gmail.com> <20260921120526.GV106095@black.igk.intel.com> <20260921170456.53354-1-navonjohnlukose@gmail.com> <20260922065041.GC106095@black.igk.intel.com> Precedence: bulk X-Mailing-List: linux-i2c@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Tue, Sep 22, 2026 at 08:50:41AM +0200, Mika Westerberg wrote: > Yes power savings are always good but in this case it also affects the > latency visible to the user so we don't want devices like touchpads become > "sluggish" either. Do you see any such issues with the devices when you > have this enabled and not using /dev/cpu_dma_latency or any other interface > to limit the CPU low power states? No. I have been running it as my only kernel for a week with nothing set on cpu_dma_latency, and I cannot tell the difference on the touchpad. This patch increases latency by 0.7 ms on the mean, which I don't think is easily noticeable by humans. Against that, the i2c traffic alone cost 2.24 W on the machine I measured, more than its entire 1.87 W idle draw. However, if anyone tests and can feel the difference, please let me know. Also, i2c_dw_configure_mode() sets TX_TL to half the FIFO and RX_TL to 0 on adjacent lines, so a transmit interrupt moves up to half a FIFO of data and a receive interrupt moves one byte, which is what this patch changes.