[PATCH 2/2] soc: qcom: apr: Publish GPR callback before client probe

[Mohit Sharma]

A GPR service driver can issue synchronous commands from its probe path,
or populate child devices which issue commands before the parent probe
returns. The APR/GPR bus currently installs the GPR service callback only
after the service driver's probe has completed.

If a response arrives while the client probe is still running, GPR finds
the destination service but cannot dispatch the response because the
service callback is NULL. The client waiting for the response eventually
times out.

This was observed intermittently on Qualcomm Lemans and Monaco platforms
when q6apm child probing sent an APM shared-memory map command before the
parent probe returned. The failure has the following signature:

  qcom-apm ... CMD timeout for [100100c] opcode
  q6apm-dai ... Audio Start: Buffer Allocation failed rc = -110
  snd-sc8280xp ... ASoC: can't create pcm MultiMedia1 Playback :-110

Install the GPR callback before invoking the client probe so responses to
probe-time commands can be dispatched. Clear the callback again if probe
fails, and preserve the existing callback ordering for APR clients.

Fixes: ec1471a898cc ("soc: qcom: apr: Add GPR support")
Cc: stable@xxxxxxxxxxxxxxx
Co-developed-by: Ajay Kumar Nandam <ajay.nandam@xxxxxxxxxxxxxxxx>
Signed-off-by: Ajay Kumar Nandam <ajay.nandam@xxxxxxxxxxxxxxxx>
Signed-off-by: Mohit Sharma <mohit.sharma@xxxxxxxxxxxxxxxx>
---
 drivers/soc/qcom/apr.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/soc/qcom/apr.c b/drivers/soc/qcom/apr.c
index ea7f83916d8d..829e5c8fdf98 100644
--- a/drivers/soc/qcom/apr.c
+++ b/drivers/soc/qcom/apr.c
@@ -365,13 +365,24 @@ static int apr_device_probe(struct device *dev)
 {
 	struct apr_device *adev = to_apr_device(dev);
 	struct apr_driver *adrv = to_apr_driver(dev->driver);
+	struct packet_router *apr = dev_get_drvdata(dev->parent);
 	int ret;
 
+	if (apr->type == PR_TYPE_GPR)
+		adev->svc.callback = adrv->gpr_callback;
+
 	ret = adrv->probe(adev);
-	if (!ret)
+	if (ret) {
+		if (apr->type == PR_TYPE_GPR)
+			adev->svc.callback = NULL;
+
+		return ret;
+	}
+
+	if (apr->type != PR_TYPE_GPR)
 		adev->svc.callback = adrv->gpr_callback;
 
-	return ret;
+	return 0;
 }
 
 static void apr_device_remove(struct device *dev)
-- 
2.34.1