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

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Date:   Mon, 1 Feb 2021 15:50:44 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        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 29/01/2021 19:33, Pierre-Louis Bossart wrote:
> 
> 
> 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?

I meant read/writes are waiting for completion interrupt!

> 
>> 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 read/writes are waiting for an interrupt, it becomes difficult to 
read or write to any registers from same interrupt handler!


> 
>> +    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.

This is magic value for each fifo read or write, so that we can verify 
that them by comparing with this magic value!

This has nothing to do with device number!

> 
>> +    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?

Qcom controllers does not provide that information if the command is 
ignored or failed by any means!

That was the behavior from the starting of this driver.

> 
>> +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?

I will try to simplify this in next version!