linux-kernel - Re: [PATCH] clk: qcom: clk-rpmh: Wait for completion when enabling clocks

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Message-ID: <20200215073233.GR955802@ripper>
Date:   Fri, 14 Feb 2020 23:32:33 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Mike Tipton <mdtipton@...eaurora.org>
Cc:     sboyd@...nel.org, tdas@...eaurora.org, mturquette@...libre.com,
        agross@...nel.org, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: qcom: clk-rpmh: Wait for completion when enabling
 clocks

On Fri 14 Feb 18:12 PST 2020, Mike Tipton wrote:

> The current implementation always uses rpmh_write_async, which doesn't
> wait for completion. That's fine for disable requests since there's no
> immediate need for the clocks and they can be disabled in the
> background. However, for enable requests we need to ensure the clocks
> are actually enabled before returning to the client. Otherwise, clients
> can end up accessing their HW before the necessary clocks are enabled,
> which can lead to bus errors.
> 
> Use the synchronous version of this API (rpmh_write) for enable requests
> in the active set to ensure completion.
> 
> Completion isn't required for sleep/wake sets, since they don't take
> effect until after we enter sleep. All rpmh requests are automatically
> flushed prior to entering sleep.
> 
> Fixes: 9c7e47025a6b ("clk: qcom: clk-rpmh: Add QCOM RPMh clock driver")
> Signed-off-by: Mike Tipton <mdtipton@...eaurora.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> ---
>  drivers/clk/qcom/clk-rpmh.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/qcom/clk-rpmh.c b/drivers/clk/qcom/clk-rpmh.c
> index 12bd8715dece..3137595a736b 100644
> --- a/drivers/clk/qcom/clk-rpmh.c
> +++ b/drivers/clk/qcom/clk-rpmh.c
> @@ -143,6 +143,19 @@ static inline bool has_state_changed(struct clk_rpmh *c, u32 state)
>  		!= (c->aggr_state & BIT(state));
>  }
>  
> +static int clk_rpmh_send(struct clk_rpmh *c, enum rpmh_state state,
> +			 struct tcs_cmd *cmd, bool wait_for_completion)
> +{
> +	int ret;
> +
> +	if (wait_for_completion)
> +		ret = rpmh_write(c->dev, state, cmd, 1);
> +	else
> +		ret = rpmh_write_async(c->dev, state, cmd, 1);
> +
> +	return ret;
> +}
> +
>  static int clk_rpmh_send_aggregate_command(struct clk_rpmh *c)
>  {
>  	struct tcs_cmd cmd = { 0 };
> @@ -159,7 +172,8 @@ static int clk_rpmh_send_aggregate_command(struct clk_rpmh *c)
>  			if (cmd_state & BIT(state))
>  				cmd.data = on_val;
>  
> -			ret = rpmh_write_async(c->dev, state, &cmd, 1);
> +			ret = clk_rpmh_send(c, state, &cmd,
> +				cmd_state && state == RPMH_ACTIVE_ONLY_STATE);
>  			if (ret) {
>  				dev_err(c->dev, "set %s state of %s failed: (%d)\n",
>  					!state ? "sleep" :
> @@ -267,7 +281,7 @@ static int clk_rpmh_bcm_send_cmd(struct clk_rpmh *c, bool enable)
>  	cmd.addr = c->res_addr;
>  	cmd.data = BCM_TCS_CMD(1, enable, 0, cmd_state);
>  
> -	ret = rpmh_write_async(c->dev, RPMH_ACTIVE_ONLY_STATE, &cmd, 1);
> +	ret = clk_rpmh_send(c, RPMH_ACTIVE_ONLY_STATE, &cmd, enable);
>  	if (ret) {
>  		dev_err(c->dev, "set active state of %s failed: (%d)\n",
>  			c->res_name, ret);
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project