Re: [alsa-devel] [PATCH 16/39] firewire-lib: Add some AV/C general commands

Takashi Sakamoto wrote:

This commit adds three commands, which may be used by some firewire device drivers. These commands are defined in 'AV/C Digital Interface Command Set General Specification Version 4.2 (2004006, 1394TA)'.

1. PLUG INFO command (10.1)
2. INPUT PLUG SIGNAL FORMAT command (10.10)
3. OUTPUT PLUG SIGNAL FORMAT command (10.11)

By the command 1, the drivers can get the number of plugs for AV/C unit or subunit. By the command 2 and 3, the drivers can get/set sampling frequency.

All these functions return errors with two different mechanisms, the AV/C response code or a negative Linux error code. This forces the caller to add a second error check that duplicates the one inside the function:

• err = avc_general_set_sig_fmt(fwspk->unit, params_rate(hw_params),

• 		      AVC_GENERAL_PLUG_DIR_IN, 0);
  

  if (err < 0) goto err_buffer;
• if (err != 0x09 /* ACCEPTED */) {

• dev_err(&fwspk->unit->device, "failed to set sample rate\n");
  

• err = -EIO;
  

• goto error;
  

• }

Would there be problems if any response except ACCEPTED resulted in -EIO?

(And here, error should be err_buffer.)

Regards, Clemens