linux-kernel - Re: [PATCH 5/6] soundwire: qcom: update register read/write routine

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Date:   Fri, 29 Jan 2021 13:33:30 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        vkoul@...nel.org
Cc:     yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [PATCH 5/6] soundwire: qcom: update register read/write routine



On 1/29/21 11:32 AM, Srinivas Kandagatla wrote:
> In the existing code every soundwire register read and register write
> are kinda blocked. Each of these are using a special command id that

what does 'kinda blocked' mean?

> generates interrupt after it successfully finishes. This is really
> overhead, limiting and not really necessary unless we are doing
> something special.
> 
> We can simply read/write the fifo that should also give exactly
> what we need! This will also allow to read/write registers in
> interrupt context, which was not possible with the special
> command approach.

This is really unclear, sorry.

> +	if (id != SWR_BROADCAST_CMD_ID) {
> +		if (id < 14)
> +			id += 1;
> +		else
> +			id = 0;

that is really odd. if id=13 (group2) then id becomes 14 (master 
address). A comment is really needed here.

> +	if (cmd_id == SWR_BROADCAST_CMD_ID) {
> +		/*
> +		 * sleep for 10ms for MSM soundwire variant to allow broadcast
> +		 * command to complete.

that's also super-odd. There is nothing in SoundWire that makes any 
difference between a regular and a broadcast command. they all complete 
in the same time (a frame).
> +		 */
> +		ret = wait_for_completion_timeout(&swrm->broadcast, (2 * HZ/10));

is this 10ms really or dependent on CONFIG_HZ?

> +		if (!ret)
> +			ret = SDW_CMD_IGNORED;
> +		else
> +			ret = SDW_CMD_OK;

no CMD_FAILED support?

> +static int qcom_swrm_cmd_fifo_rd_cmd(struct qcom_swrm_ctrl *swrm,
> +				     u8 dev_addr, u16 reg_addr,
> +				     u32 len, u8 *rval)
> +{
> +	u32 val;
> +	u32 retry_attempt = 0;
> +	u32 cmd_data;
> +	int ret = SDW_CMD_OK;
> +
> +	mutex_lock(&swrm->io_lock);
> +	val = swrm_get_packed_reg_val(&swrm->rcmd_id, len, dev_addr, reg_addr);
> +
> +	/* wait for FIFO RD to complete to avoid overflow */
> +	usleep_range(100, 105);
> +	swrm->reg_write(swrm, SWRM_CMD_FIFO_RD_CMD, val);
> +	/* wait for FIFO RD CMD complete to avoid overflow */
> +	usleep_range(250, 255);
> +
> +retry_read:
> +
> +	swrm->reg_read(swrm, SWRM_CMD_FIFO_RD_FIFO_ADDR, &cmd_data);
> +	rval[0] = cmd_data & 0xFF;
> +
> +	if ((((cmd_data) & 0xF00) >> 8) != swrm->rcmd_id) {
> +		if (retry_attempt < MAX_FIFO_RD_FAIL_RETRY) {
> +			/* wait 500 us before retry on fifo read failure */
> +			usleep_range(500, 505);
> +			if (retry_attempt == (MAX_FIFO_RD_FAIL_RETRY - 1)) {
> +				swrm->reg_write(swrm, SWRM_CMD_FIFO_CMD, 0x1);
> +				swrm->reg_write(swrm, SWRM_CMD_FIFO_RD_CMD, val);
> +			}
> +			retry_attempt++;
> +			goto retry_read;
> +		} else {
> +			dev_err(swrm->dev,
> +					"failed to read fifo: reg: 0x%x, \
> +					rcmd_id: 0x%x, dev_num: 0x%x, cmd_data: 0x%x\n",
> +					reg_addr, swrm->rcmd_id,
> +					dev_addr, cmd_data);
> +			ret = SDW_CMD_IGNORED;
> +		}
>   	}

the flow seems complicated with multiple tests and goto? Can this be 
simplified?