Re: [PATCH] ata: add AMD Seattle platform driver

[Brijesh Singh <brijesh.singh@amd.com>]

Hi,

On 01/07/2016 05:42 PM, Arnd Bergmann wrote:
> On Thursday 07 January 2016 16:24:22 Brijesh Singh wrote:
>>>> +
>>>> +Examples:
>>>> +        sata0@e0300000 {
>>>> +            compatible = "amd,seattle-ahci";
>>>> +            reg = <0x0 0xe0300000 0x0 0xf0000>, <0x0 0xe0000078 0x0 0x1>;
>>>
>>> Looking at the register values, I doubt that the SGPIO is actually part of the
>>> sata device. More likely, you are pointing in the middle of an actual
>>> GPIO controller.
>>>
>>
>> That address is SGPIO control register for SATA. The current hardware implementation to control activity LED is not ideal.
>
> Of course its a control register "for" SATA, what I meant is that it's
> not part "of" the SATA IP block, which is hopefully a standard AHCI
> compliant part as required by SBSA.
>
Yes, its not part of SATA IP block. We just need a method of pass  SGPIO 
control register address to driver.

Should I consider adding a property "sgpio-ctrl" to pass the register 
address ?

e.g

sata0@e0300000 {
   compatible = "amd,seattle-ahci";
   reg = <0 0xe0300000 0 0x800>;
   amd,sgpio-ctrl = <0xe0000078>;
   interrupts = <0 355 4>;
   clocks = <&sataclk_333mhz>;
   dma-coherent;
};


>> A57 does not have access to GPIO's connected to backplane controller
>> instead SoC has exposed two SGPIO control registers (LSIOC_SGPIO_CONTROL0:
>> 0xE000_0078 and LSIOC_SGPIO_CONTROL1: 0xE000_007C) to A57. All we
>> need to do is to program these registers based on the disk activity.
>> The firmware running on A5 reads the values and generate proper SGPIO
>> timing and toggles the LEDs etc.
>
> It still sounds like SGPIO is not part of the AHCI standard spec, but
> rather a subset of a device called LSIOC.
>
>> These registers are defined in SATA0/1 DSDT resource template and also
>> documented in SoC BKDG. I just noticed that BKDG has wrong register
>> definition so will ask documentation folks to fix that.
>>
>> This driver is using SGPIO LED control similar to sata_highbank [1]
>> except bit bang GPIO (which is done by firmware).
>>
>> [1] http://lxr.free-electrons.com/source/drivers/ata/sata_highbank.c#L140
>
> This one is rather different: there is a single device that combines
> registers for AHCI, the PHY attached to it and the LED. This is not
> SBSA compliant of course, and it requires having a special driver.
>
> What you have instead looks like a regular AHCI implementation that
> should just work with the standard driver as long as you describe how
> it gets its LEDs.
>
Yes, its regular AHCI implementation and works well with ahci_platform 
driver. In standard ahci_platform driver activity LEDs are blinked 
through enclosure management interface. Given the current hardware 
limitation it seems like creating a new driver would be cleaner. I am 
open to suggestion.

Thanks for all your review feedbacks.

> 	Arnd
>