2015-10-15 17:40 GMT+08:00 Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>: > On Thu, 2015-10-15 at 11:32 +0300, Jarkko Nikula wrote: >> On 10/15/2015 08:46 AM, Xiang Wang wrote: >> > >> > In conclusion, we have 2 solutions to set the i2c controller speed >> > mode (pci driver): >> > 1) use hardcode value in pci driver >> > 2) use frequency setting of "i2c device" in ACPI table (more >> > flexible, >> > but looks a bit strange) >> > >> > Do you have any preference/suggestions for above solutions? Thanks >> >> I don't think we can hard code especially the high-speed mode because >> >> most typically buses are populated with slower devices. >> >> Things are a bit more clear when ACPI provides timing parameters for >> the >> bus (for standard and fast speed modes at the moment in >> i2c-designware-platdrv.c: dw_i2c_acpi_configure()) but still I think >> the >> ACPI namespace walk may be needed against potential BIOS >> misconfigurations. For instance if it provides timing parameters for >> all >> speeds but there are devices with lower speed on the same bus. >> >> I'd take these timing parameters as configuration data for bus >> features >> but actual speed (speed bits in IC_CON register) is defined >> separately. >> To me it looks only way to achieve that is to pick slowest device >> from >> I2cSerialBus resource descriptors. > > Should it (ACPI walk) be done in PCI case as well? If so, then it needs > to be done up to i2c-core. There you may adjust the bus speed whenever > slave device is enumerated. > I think the "ACPI walk for bus speed" also works for PCI case. It'll be good to do this in i2c-core. By doing this we can get a minimum device speed for this bus. I2C bus drivers can use this speed to set corresponding mode into i2c controller. Waiting for comments from others. > For PCI case you have still to have hardcoded values and it should be > maximum supported by the bus I think. When you have implemented above > algorithm you may do this safely. Am I missing something? Agree. It'll be safer to set a hardcoded maximum supported speed of the bus for PCI case. I2C bus driver can use MIN(speed_get_by_ACPI_walk, hardcoded_max_supported_speed) for bus speed. > > -- > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Intel Finland Oy -- Regards, Xiang -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
