Re: [PATCH 2/3] ASoC: SOF: imx: Add i.MX8 HW support

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 8/17/19 10:21 AM, Cezary Rojewski wrote:
> On 2019-08-15 17:44, Pierre-Louis Bossart wrote:
>> From: Daniel Baluta <daniel.baluta@nxp.com>
>>
>> Add support for the audio DSP hardware found on NXP i.MX8 platform.
>>
>> Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
>> Signed-off-by: Pierre-Louis Bossart 
>> <pierre-louis.bossart@linux.intel.com>
>> +static void imx8_get_reply(struct snd_sof_dev *sdev)
>> +{
>> +    struct snd_sof_ipc_msg *msg = sdev->msg;
>> +    struct sof_ipc_reply reply;
>> +    int ret = 0;
>> +
>> +    if (!msg) {
>> +        dev_warn(sdev->dev, "unexpected ipc interrupt\n");
>> +        return;
>> +    }
>> +
>> +    /* get reply */
>> +    sof_mailbox_read(sdev, sdev->host_box.offset, &reply, 
>> sizeof(reply));
>> +
>> +    if (reply.error < 0) {
>> +        memcpy(msg->reply_data, &reply, sizeof(reply));
>> +        ret = reply.error;
>> +    } else {
>> +        /* reply has correct size? */
>> +        if (reply.hdr.size != msg->reply_size) {
>> +            dev_err(sdev->dev, "error: reply expected %zu got %u 
>> bytes\n",
>> +                msg->reply_size, reply.hdr.size);
>> +            ret = -EINVAL;
>> +        }
>> +
>> +        /* read the message */
>> +        if (msg->reply_size > 0)
>> +            sof_mailbox_read(sdev, sdev->host_box.offset,
>> +                     msg->reply_data, msg->reply_size);
>> +    }
>> +
>> +    msg->reply_error = ret;
>> +}
> 
> Assuming reply.hdr.size is coming from HW IPC regs, msg object is 
> representing application side - SW, kernel. If so, is msg->reply_size 
> value an estimated size (which can be overestimated since exact size may 
> be unknown by the host) -or- the exact size of incoming IPC reply?
> 
> The estimated-case is usually permissive as long as assumed size is >= 
> reply.hdr.size - dev_err needed. In the exact-case, it should be viewed 
> as a requirement. If such "requirement" fails, is it valid to read 
> mailbox regardless? Is this to extract some error-debug payload sent by FW?
> 
> Just curious, please feel free to correct me here, Pierre.

I don't quite understand the question. There is no use of HW IPC 
registers (as done in SKL) since this is not portable across hardware. 
There *may* be information sent over IPC registers but that would have 
to be done in platform-specific ways - as will be done for Intel to e.g. 
avoid using memory windows that may not be powered.
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