On Wednesday 02 March 2016 09:05:49 Michal Simek wrote: > On 2.3.2016 06:53, Anurag Kumar Vulisha wrote: > >>>>> > >>>>> I would probably make this dependent on the compatible string > >>>>> instead, and have a table in the device driver that uses a > >>>>> specific value for each variant of the device, but either way should be > >> fine. > >>>>> > >>>>> Having a separate property is most appropriate if for each > >>>>> hardware revision there is exactly one ideal value, while a table > >>>>> in the driver makes more sense if this takes a bit of tuning and > >>>>> the driver might choose to optimize it differently based on other > >>>>> constraints, such as its own interrupt handler implementation. > > that 0x40 is value choose based on testing that it is not causing any > visible problem and this is used as default value in the driver > (PTC_RX_WM_VAL - ahci_ceva.c) > > Values which you can setup are in range 0x0 - 0x7f (7bits). It means > hardware fifo size is probably 0x80. > > And this dt/module parameter is IMHO just sw setting setup by user. > It means I am not quite sure that this is DT parameter because it is > just SW setting. > I expect this range will be valid for all silicon revisions. > If happen that any silicon revision can't setup certain level because of > HW bug we can handle it via DT parameter or specific compatible string. > But setting up watermark SW level via DT doesn't look correct to me. > > Please let me know what you think. Ok, thanks for the background. I think we should just leave it to be set by the driver then. Please make sure that each SoC specific .dtsi file has a unique "compatible" string for the device though, so that the driver can later override it based on the specific variant if that ends up being necessary for performance or bug-avoidance. Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
