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ACPI SSCN/FMCN methods were originally added because then the platform can provide the most accurate HCNT/LCNT values to the driver. However, this seems not to be true for Dell Inspiron 7348 where using these causes the touchpad to fail in boot: i2c_hid i2c-DLL0675:00: failed to retrieve report from device. i2c_designware INT3433:00: i2c_dw_handle_tx_abort: lost arbitration i2c_hid i2c-DLL0675:00: failed to retrieve report from device. i2c_designware INT3433:00: controller timed out The values received from ACPI are (in fast mode): HCNT: 72 LCNT: 160 this translates to following timings (input clock is 100MHz on Broadwell): tHIGH: 720 ns (spec min 600 ns) tLOW: 1600 ns (spec min 1300 ns) Bus period: 2920 ns (assuming 300 ns tf and tr) Bus speed: 342.5 kHz Both tHIGH and tLOW are within the I2C specification. The calculated values when ACPI parameters are not used are (in fast mode): HCNT: 87 LCNT: 159 which translates to: tHIGH: 870 ns (spec min 600 ns) tLOW: 1590 ns (spec min 1300 ns) Bus period 3060 ns (assuming 300 ns tf and tr) Bus speed 326.8 kHz These values are also within the I2C specification. Since both ACPI and calculated values meet the I2C specification timing requirements it is hard to say why the touchpad does not function properly with the ACPI values except that the bus speed is higher in this case (but still well below the max 400kHz). Solve this by adding DMI quirk to the driver that disables using ACPI parameters on this particulare machine. Reported-by: Pavel Roskin <plroskin@gmail.com> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com> Tested-by: Pavel Roskin <plroskin@gmail.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de> Cc: stable@kernel.org |
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| .. | ||
| algos | ||
| busses | ||
| muxes | ||
| i2c-boardinfo.c | ||
| i2c-core.c | ||
| i2c-core.h | ||
| i2c-dev.c | ||
| i2c-mux.c | ||
| i2c-slave-eeprom.c | ||
| i2c-smbus.c | ||
| i2c-stub.c | ||
| Kconfig | ||
| Makefile | ||