linux-kernel - Re: [PATCH 11/11] firmware: arm_scmi: Use asynchronous CLOCK_RATE

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Message-Id: <20190722212954.8924D21900@mail.kernel.org>
Date:   Mon, 22 Jul 2019 14:29:53 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Sudeep Holla <sudeep.holla@....com>, linux-kernel@...r.kernel.org,
        Peng Fan <peng.fan@....com>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        Bo Zhang <bozhang.zhang@...adcom.com>,
        Volodymyr Babchuk <volodymyr_babchuk@...m.com>
Subject: Re: [PATCH 11/11] firmware: arm_scmi: Use asynchronous CLOCK_RATE_SET when possible

Quoting Sudeep Holla (2019-07-08 08:47:30)
> CLOCK_PROTOCOL_ATTRIBUTES provides attributes to indicate the maximum
> number of pending asynchronous clock rate changes supported by the
> platform. If it's non-zero, then we should be able to use asynchronous
> clock rate set for any clocks until the maximum limit is reached.
> 
> Keeping the current count of pending asynchronous clock set rate
> requests, we can decide if we can you asynchronous request for the

This last part of the sentence doesn't read properly. Please rewrite.

> incoming/new request.
> 
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/firmware/arm_scmi/clock.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/firmware/arm_scmi/clock.c b/drivers/firmware/arm_scmi/clock.c
> index dd215bd11a58..70044b7c812e 100644
> --- a/drivers/firmware/arm_scmi/clock.c
> +++ b/drivers/firmware/arm_scmi/clock.c
> @@ -221,21 +222,35 @@ static int scmi_clock_rate_set(const struct scmi_handle *handle, u32 clk_id,
>                                u64 rate)
>  {
>         int ret;
> +       u32 flags = 0;
>         struct scmi_xfer *t;
>         struct scmi_clock_set_rate *cfg;
> +       struct clock_info *ci = handle->clk_priv;
>  
>         ret = scmi_xfer_get_init(handle, CLOCK_RATE_SET, SCMI_PROTOCOL_CLOCK,
>                                  sizeof(*cfg), 0, &t);
>         if (ret)
>                 return ret;
>  
> +       if (ci->max_async_req) {
> +               if (atomic_inc_return(&ci->cur_async_req) < ci->max_async_req)
> +                       flags |= CLOCK_SET_ASYNC;
> +               else
> +                       atomic_dec(&ci->cur_async_req);

Can this be combined with the atomic_dec() below and done after either
transfer?

> +       }
> +
>         cfg = t->tx.buf;
> -       cfg->flags = cpu_to_le32(0);
> +       cfg->flags = cpu_to_le32(flags);
>         cfg->id = cpu_to_le32(clk_id);
>         cfg->value_low = cpu_to_le32(rate & 0xffffffff);
>         cfg->value_high = cpu_to_le32(rate >> 32);
>  
> -       ret = scmi_do_xfer(handle, t);
> +       if (flags & CLOCK_SET_ASYNC) {
> +               ret = scmi_do_xfer_with_response(handle, t);
> +               atomic_dec(&ci->cur_async_req);
> +       } else {
> +               ret = scmi_do_xfer(handle, t);
> +       }

I mean putting the atomic_dec() here.

>  
>         scmi_xfer_put(handle, t);
>         return ret;