Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree

Arnd Bergmann
2016-02-20T22:34:41Z

On Saturday 20 February 2016 18:48:22 Anurag Kumar Vulisha wrote:
> index 7ca8b97..7e48dfc 100644
> --- a/Documentation/devicetree/bindings/ata/ahci-ceva.txt
> +++ b/Documentation/devicetree/bindings/ata/ahci-ceva.txt
> @@ -8,6 +8,7 @@ Required properties:
>
> Optional properties:
> - ceva,broken-gen2: limit to gen1 speed instead of gen2.
> + - ceva,rx-watermark: RX fifo water mark level for SATA controller.
>
> Examples:
> ahci@fd0c0000 {
> @@ -17,4 +18,5 @@ Examples:
> interrupts = <0 133 4>;
> clocks = <&clkc SATA_CLK_ID>;
> ceva,broken-gen2;
> + ceva,rx-watermark = <0x40>;
> };
>

How would a hardware integrator know which value is right for a
particular SoC?

Could it be keyed off the hardware ID? Could the bootloader
perhaps set an appropriate value in the AHCI_VEND_PTC
register at boot time and the driver read the initial
value from it?

>From the description, it sounds like this is a policy decision
rather than hardware description, and shouldn't really be
in here.

Arnd