[PATCH] dmaengine: cppi41: Fix cppi41_dma_prep_slave_sg() when idle

From: Tony Lindgren <tony@atomide.com>
To: Dan Williams <dan.j.williams@intel.com>,
	Vinod Koul <vinod.koul@intel.com>
Cc: Alexandre Bailon <abailon@baylibre.com>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	Bin Liu <b-liu@ti.com>, Daniel Mack <zonque@gmail.com>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	George Cherian <george.cherian@ti.com>,
	Grygorii Strashko <grygorii.strashko@ti.com>,
	Johan Hovold <johan@kernel.org>,
	Peter Ujfalusi <peter.ujfalusi@ti.com>,
	Sekhar Nori <nsekhar@ti.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>,
	dmaengine@vger.kernel.org, linux-usb@vger.kernel.org,
	linux-omap@vger.kernel.org,
	giulio.benetti@benettiengineering.com,
	Sebastian Reichel <sre@kernel.org>,
	Skvortsov <andrej.skvortzov@gmail.com>,
	Yegor Yefremov <yegorslists@googlemail.com>
Subject: [PATCH] dmaengine: cppi41: Fix cppi41_dma_prep_slave_sg() when idle
Date: Wed, 23 Oct 2019 08:31:38 -0700	[thread overview]
Message-ID: <20191023153138.23442-1-tony@atomide.com> (raw)

Yegor Yefremov <yegorslists@googlemail.com> reported that musb and ftdi
uart can fail for the first open of the uart unless connected using
a hub.

This is because the first dma call done by musb_ep_program() must wait
if cppi41 is PM runtime suspended. Otherwise musb_ep_program() continues
with other non-dma packets before the DMA transfer is started causing at
least ftdi uarts to fail to receive data.

Let's fix the issue by waking up cppi41 with PM runtime calls added to
cppi41_dma_prep_slave_sg() and return NULL if still idled. This way we
have musb_ep_program() continue with PIO until cppi41 is awake.

Fixes: fdea2d09b997 ("dmaengine: cppi41: Add basic PM runtime support")
Cc: Bin Liu <b-liu@ti.com>
Cc: giulio.benetti@benettiengineering.com
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Skvortsov <andrej.skvortzov@gmail.com>
Reported-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
---

Please consider adding Cc stable v4.9+ tag when committing

---
 drivers/dma/ti/cppi41.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/ti/cppi41.c b/drivers/dma/ti/cppi41.c
--- a/drivers/dma/ti/cppi41.c
+++ b/drivers/dma/ti/cppi41.c
@@ -586,9 +586,22 @@ static struct dma_async_tx_descriptor *cppi41_dma_prep_slave_sg(
 	enum dma_transfer_direction dir, unsigned long tx_flags, void *context)
 {
 	struct cppi41_channel *c = to_cpp41_chan(chan);
+	struct dma_async_tx_descriptor *txd = NULL;
+	struct cppi41_dd *cdd = c->cdd;
 	struct cppi41_desc *d;
 	struct scatterlist *sg;
 	unsigned int i;
+	int error;
+
+	error = pm_runtime_get(cdd->ddev.dev);
+	if (error < 0) {
+		pm_runtime_put_noidle(cdd->ddev.dev);
+
+		return NULL;
+	}
+
+	if (cdd->is_suspended)
+		goto err_out_not_ready;
 
 	d = c->desc;
 	for_each_sg(sgl, sg, sg_len, i) {
@@ -611,7 +624,13 @@ static struct dma_async_tx_descriptor *cppi41_dma_prep_slave_sg(
 		d++;
 	}
 
-	return &c->txd;
+	txd = &c->txd;
+
+err_out_not_ready:
+	pm_runtime_mark_last_busy(cdd->ddev.dev);
+	pm_runtime_put_autosuspend(cdd->ddev.dev);
+
+	return txd;
 }
 
 static void cppi41_compute_td_desc(struct cppi41_desc *d)
-- 
2.23.0
