linux-kernel - Re: [PATCH] soundwire: qcom: wait for fifo space to be available before read/write

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Date:   Wed, 31 Mar 2021 13:38:32 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        vkoul@...nel.org
Cc:     robh@...nel.org, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        sanyog.r.kale@...el.com, yung-chuan.liao@...ux.intel.com
Subject: Re: [PATCH] soundwire: qcom: wait for fifo space to be available
 before read/write


> +static int swrm_wait_for_rd_fifo_avail(struct qcom_swrm_ctrl *swrm)
> +{
> +	u32 fifo_outstanding_cmd, value;
> +	u8 fifo_retry_count = SWR_OVERFLOW_RETRY_COUNT;
> +
> +	/* Check for fifo underflow during read */
> +	swrm->reg_read(swrm, SWRM_CMD_FIFO_STATUS, &value);
> +	fifo_outstanding_cmd = FIELD_GET(SWRM_RD_CMD_FIFO_CNT_MASK, value);
> +
> +	 /* Check number of outstanding commands in fifo before read */
> +	if (fifo_outstanding_cmd)
> +		return 0;
> +
> +	do {
> +		usleep_range(500, 510);
> +		swrm->reg_read(swrm, SWRM_CMD_FIFO_STATUS, &value);
> +		fifo_outstanding_cmd = FIELD_GET(SWRM_RD_CMD_FIFO_CNT_MASK, value);
> +		if (fifo_outstanding_cmd > 0)
> +			break;
> +	} while (fifo_retry_count--);
> +
> +	if (fifo_outstanding_cmd == 0) {
> +		dev_err_ratelimited(swrm->dev, "%s err read underflow\n", __func__);
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +static int swrm_wait_for_wr_fifo_avail(struct qcom_swrm_ctrl *swrm)
> +{
> +	u32 fifo_outstanding_cmd, value;
> +	u8 fifo_retry_count = SWR_OVERFLOW_RETRY_COUNT;
> +
> +	/* Check for fifo overflow during write */
> +	swrm->reg_read(swrm, SWRM_CMD_FIFO_STATUS, &value);
> +	fifo_outstanding_cmd = FIELD_GET(SWRM_WR_CMD_FIFO_CNT_MASK, value);
> +
> +	/* Check number of outstanding commands in fifo before write */
> +	if (fifo_outstanding_cmd != swrm->wr_fifo_depth)
> +		return 0;
> +
> +	do {
> +		usleep_range(500, 510);
> +		swrm->reg_read(swrm, SWRM_CMD_FIFO_STATUS, &value);
> +		fifo_outstanding_cmd = FIELD_GET(SWRM_WR_CMD_FIFO_CNT_MASK, value);
> +		if (fifo_outstanding_cmd < swrm->wr_fifo_depth)
> +			break;
> +	} while (fifo_retry_count--);
> +
> +	if (fifo_outstanding_cmd == swrm->wr_fifo_depth) {
> +		dev_err_ratelimited(swrm->dev, "%s err write overflow\n", __func__);
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}

nit-pick: you could merge the prologue and loop body with a 
while(fifo_retry_count--) and put the usleep_range() at the end of the loop.