Re: [Xen-devel] [RFC V2] xen: interface: introduce pvclk interface

[Peng Fan <van.freenix@xxxxxxxxx>]

Hi Juergen,

On Wed, Jan 20, 2016 at 10:05:15AM +0100, Juergen Gross wrote:
>On 20/01/16 09:31, Peng Fan wrote:
>> Introduce pvclk interface which is useful when doing device passthrough
>> on ARM platform.
>
>...
>
>> +/*
>> + * Frontend request
>> + *
>> + * cmd: command for operation on clk, should be XEN_CLK_[xx],
>> + *  excluding XEN_CLK_END. id is the
>> + * id: clk id
>> + * rate: clock rate. Used for set rate.
>
>Which unit? Hz?

Yeah. Hz. I'll add comments in V3.

>
>> + */
>> +struct xen_clkif_request {
>> +    uint32_t cmd;
>> +    uint32_t id;
>> +    uint64_t rate;
>> +};
>> +typedef struct xen_clkif_request xen_clkif_request_t;
>> +
>> +/*
>> + * Backend response
>> + *
>> + * cmd: command for operation on clk, same with the cmd in request.
>> + * id: clk id, same with the id in request.
>> + * success: indicate failure or success for the cmd.
>
>Values?

I'd like to let the frontend/backend driver to determine the value.
In my implementation for linux, if the backend API supports return value,
I'll fill the return value to success entry. If the backend API returns
void, I'll just fill 0 to success entry.

>
>> + * rate: clock rate. Used for get rate.
>> + *
>> + * cmd and id are filled by backend and passed to frontend to
>> + * let frontend check whether the response is for the current
>> + * request or not.
>
>I'd rather let the frontend add a request Id to the request which
>will be echoed here instead cmd and clock Id.

If using request id, I think we can encode cmd and id into request id?
To my dts case, clk id is simple. But I am not sure about ACPI part. Maybe
I can not simply encode them into request id.
Wait for more comments on this:)

Thanks,
Peng.
>
>
>Juergen

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