[RFC PATCH net v5] net: airoha: Add retry mechanism to airoha_qdma_set_trtcm_param()

[Christian Marangi <ansuelsmth@gmail.com>]

From: Brown Huang <brown.huang@airoha.com>

CPU accesses QDMA via the bus. When multiple modules are using the bus
simultaneously, CPU access to QDMA may encounter bus timeouts and fails,
resulting in QDMA configuration failures and potentially causing packet
transmission issues. In order to mitigate the issue, introduce a retry
mechanism to airoha_qdma_set_trtcm_param routine in order to ensure the
configuration is correctly applied to the hardware.

It's enough to try a second time for the TRTCM config to be actually
applied to make sure we are not in the middle of bucket handling as it does
operate on fixed time slot internally.

Fixes: ef1ca9271313b ("net: airoha: Add sched HTB offload support")
Signed-off-by: Brown Huang <brown.huang@airoha.com>
[ improve commit description, drop memory block, apply better loop logic]
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
Changes v5:
- Drop memory block (not needed)
- Loop only 2 times
- Improve description
Changes v4:
- Rebase on top of net
Changes v3:
- Init data
- Use continue instead of negative error for poll
- Add memobry block after CFG_PARAM

 drivers/net/ethernet/airoha/airoha_eth.c | 32 +++++++++++++++++++-----
 drivers/net/ethernet/airoha/airoha_eth.h |  2 ++
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index 21ac80bdd084..b164a78ddac9 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -3120,14 +3120,34 @@ static int airoha_qdma_set_trtcm_param(struct airoha_qdma *qdma, int channel,
 		     FIELD_PREP(TRTCM_METER_GROUP_MASK, group) |
 		     FIELD_PREP(TRTCM_PARAM_INDEX_MASK, idx) |
 		     FIELD_PREP(TRTCM_PARAM_RATE_TYPE_MASK, mode);
+	int i;
 
-	airoha_qdma_wr(qdma, REG_TRTCM_DATA_LOW(addr), val);
-	airoha_qdma_wr(qdma, REG_TRTCM_CFG_PARAM(addr), config);
+	/*
+	 * HW might be in the middle of bucket handling and might
+	 * require an additional try to actually apply the new TRTCM
+	 * config.
+	 */
+	for (i = 0; i < TRTCM_CONFIG_RETRY_MAX; i++) {
+		u32 data = 0;
 
-	return read_poll_timeout(airoha_qdma_rr, val,
-				 val & TRTCM_PARAM_RW_DONE_MASK,
-				 USEC_PER_MSEC, 10 * USEC_PER_MSEC, true,
-				 qdma, REG_TRTCM_CFG_PARAM(addr));
+		airoha_qdma_wr(qdma, REG_TRTCM_DATA_LOW(addr), val);
+		airoha_qdma_wr(qdma, REG_TRTCM_CFG_PARAM(addr), config);
+
+		if (read_poll_timeout(airoha_qdma_rr, data,
+				      data & TRTCM_PARAM_RW_DONE_MASK,
+				      USEC_PER_MSEC, 10 * USEC_PER_MSEC,
+				      true, qdma, REG_TRTCM_CFG_PARAM(addr)))
+			continue;
+
+		if (airoha_qdma_get_trtcm_param(qdma, channel, addr, param,
+						mode, &data, NULL))
+			continue;
+
+		if (data == val)
+			return 0;
+	}
+
+	return -EBUSY;
 }
 
 static int airoha_qdma_set_trtcm_config(struct airoha_qdma *qdma, int channel,
diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index 286f73e2e1e0..d270729e22ff 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h
@@ -184,6 +184,8 @@ enum trtcm_param {
 #define TRTCM_TOKEN_RATE_MASK			GENMASK(23, 6)
 #define TRTCM_TOKEN_RATE_FRACTION_MASK		GENMASK(5, 0)
 
+#define TRTCM_CONFIG_RETRY_MAX			2
+
 enum airoha_dma_map_type {
 	AIROHA_DMA_UNMAPPED,
 	AIROHA_DMA_MAP_SINGLE,
-- 
2.55.0