linux-kernel - [PATCH] dmaengine: of-dma: router_xlate to return -EPROBE

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Date:   Sat, 17 Jul 2021 22:00:21 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...il.com>
To:     vkoul@...nel.org
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, tony@...mide.com, nm@...com
Subject: [PATCH] dmaengine: of-dma: router_xlate to return -EPROBE_DEFER if controller is not yet available

If the router_xlate can not find the controller in the available DMA
devices then it should return with -EPORBE_DEFER in a same way as the
of_dma_request_slave_channel() does.

The issue can be reproduced if the event router is registered before the
DMA controller itself and a driver would request for a channel before the
controller is registered.
In of_dma_request_slave_channel():
1. of_dma_find_controller() would find the dma_router
2. ofdma->of_dma_xlate() would fail and returned NULL
3. -ENODEV is returned as error code

with this patch we would return in this case the correct -EPROBE_DEFER and
the client can try to request the channel later.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...il.com>
---
Hi,

I have noticed the descibed failure sequence on Beagle-x15 board (McASP fails to
probe). It must have been broken for some time, I have not booted the board for
about a year or so...

Regards,
Peter

 drivers/dma/of-dma.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
index ec00b20ae8e4..ac61ecda2926 100644
--- a/drivers/dma/of-dma.c
+++ b/drivers/dma/of-dma.c
@@ -67,8 +67,12 @@ static struct dma_chan *of_dma_router_xlate(struct of_phandle_args *dma_spec,
 		return NULL;

 	ofdma_target = of_dma_find_controller(&dma_spec_target);
-	if (!ofdma_target)
-		return NULL;
+	if (!ofdma_target) {
+		ofdma->dma_router->route_free(ofdma->dma_router->dev,
+					      route_data);
+		chan = ERR_PTR(-EPROBE_DEFER);
+		goto err;
+	}

 	chan = ofdma_target->of_dma_xlate(&dma_spec_target, ofdma_target);
 	if (IS_ERR_OR_NULL(chan)) {
@@ -89,6 +93,7 @@ static struct dma_chan *of_dma_router_xlate(struct of_phandle_args *dma_spec,
 		}
 	}

+err:
 	/*
 	 * Need to put the node back since the ofdma->of_dma_route_allocate
 	 * has taken it for generating the new, translated dma_spec
-- 
2.32.0