[Intel-gfx] [bug report] drm/i915/guc: Add support for data reporting in GuC responses

[Dan Carpenter]

Hello Michal Wajdeczko,

The patch b839a869dfc9: "drm/i915/guc: Add support for data reporting
in GuC responses" from Mar 26, 2018, leads to the following static
checker warning:

	drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c:307 intel_guc_ct_enable()
	error: passing non negative 4095 to ERR_PTR

drivers/gpu/drm/i915/gt/uc/.intel_guc.c
   405          intel_guc_notify(guc);
   406  
   407          /*
   408           * No GuC command should ever take longer than 10ms.
   409           * Fast commands should still complete in 10us.
   410           */
   411          ret = __intel_wait_for_register_fw(uncore,
   412                                             guc_send_reg(guc, 0),
   413                                             INTEL_GUC_MSG_TYPE_MASK,
   414                                             INTEL_GUC_MSG_TYPE_RESPONSE <<
   415                                             INTEL_GUC_MSG_TYPE_SHIFT,
   416                                             10, 10, &status);
   417          /* If GuC explicitly returned an error, convert it to -EIO */
   418          if (!ret && !INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(status))
   419                  ret = -EIO;

If __intel_wait_for_register_fw() fails then either "ret" is set or
"status" status has a code and "ret" becomes -EIO.

   420  
   421          if (ret) {
   422                  DRM_ERROR("MMIO: GuC action %#x failed with error %d %#x\n",
   423                            action[0], ret, status);
   424                  goto out;

So if there is any errors we return here.

   425          }
   426  
   427          if (response_buf) {
   428                  int count = min(response_buf_size, guc->send_regs.count - 1);
   429  
   430                  for (i = 0; i < count; i++)
   431                          response_buf[i] = intel_uncore_read(uncore,
   432                                                              guc_send_reg(guc, i + 1));
   433          }
   434  
   435          /* Use data from the GuC response as our return value */
   436          ret = INTEL_GUC_MSG_TO_DATA(status);

But this is setting "ret" to something positive in the 0xffff range.
The caller treats it as an error code.

   437  
   438  out:
   439          intel_uncore_forcewake_put(uncore, guc->send_regs.fw_domains);
   440          mutex_unlock(&guc->send_mutex);
   441  
   442          return ret;
   443  }

regards,
dan carpenter