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Sun, 04 Oct 2026 20:27:36 -0700 (PDT) From: Yuqi Xu To: Mika Westerberg Cc: westeri@kernel.org, andi.shyti@kernel.org, linux-i2c@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] i2c: acpi: Add ELAN0662 to i2c_acpi_force_100khz_device_ids Date: Mon, 5 Oct 2026 11:26:55 +0800 Message-ID: <20261005032655.12633-1-xuyuqiabc@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261005024654.26888-1-xuyuqiabc@gmail.com> References: <20260918054109.23550-1-xuyuqiabc@gmail.com> <20260918055653.GD106095@black.igk.intel.com> <20261005024654.26888-1-xuyuqiabc@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi Andi, Mika, Please don't apply this patch. I was wrong about the fix, and I'm sorry for the time already spent on it. I treated this as the same 100 kHz quirk as the other ELAN touchpads. That was a mistake. On this machine, forcing ELAN0662 to 100 kHz does not stop the touch jumps. The firmware already asks for 400 kHz. \_SB.I2CA (_HID AMDI0010) publishes the timings through _DSM. iasl marks the UUID unknown, and I could not find a public AMD specification for it: Method (_DSM, 4, Serialized) { If ((Arg0 == ToUUID ("d93e4d1c-58bb-493c-a06a-605a717f9e2e"))) { Switch (ToInteger (Arg2)) { Case (Zero) { Return (Buffer (One) { 0x03 }) } Case (One) { Return (Buffer (0x04) { 0xE5, 0x00, 0x6A, 0x00 }) } } } } The same UUID is present on other Lenovo AMD platforms. AMD's amdi2c.sys 1.2.0.126 reads function 1 as two little-endian words, LCNT 0x00E5 (229) and HCNT 0x006A (106), and programs IC_SDA_HOLD with 0x48. I could not find that layout written down anywhere else. i2c-designware does not evaluate this _DSM. It derives HCNT/LCNT from the 150 MHz input clock and leaves SDA hold at the reset value of 1. The comment above i2c_acpi_force_100khz_device_ids already suspects those default counters, and notes that Windows works at 400 kHz. Forcing 100 kHz only avoids the bad fast-mode counters. Programming the values from the _DSM changed the result: 100 kHz, SDA hold 45: touch jumps within about a minute 400 kHz, FS HCNT/LCNT 106/229, SDA hold 0x48: i2c_designware AMDI0010:00: SDA Hold Time TX:RX = 72:1 i2c_designware AMDI0010:00: Fast Mode HCNT:LCNT = 106:229 i2c_designware AMDI0010:00: Bus speed: Fast Mode (400 kHz) the same use no longer logged "Touch jump detected". So this entry does not belong in i2c_acpi_force_100khz_device_ids. The follow-up will be a separate i2c-designware patch: in i2c_dw_acpi_configure(), when SSCN/FMCN are absent, take fast-mode HCNT/LCNT from that _DSM and set SDA hold to 0x48, and leave the bus at the firmware speed. Please drop this one. Thank you for the Ack, Mika, and sorry again. Yuqi