dmaengine: cppi41: Fix cppi41_dma_prep_slave_sg() when idle

BugLink: https://bugs.launchpad.net/bugs/1852492
commit bacdcb6675e170bb2e8d3824da220e10274f42a7 upstream.

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")
Reported-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Cc: stable@vger.kernel.org # v4.9+
Link: https://lore.kernel.org/r/20191023153138.23442-1-tony@atomide.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/dma/cppi41.c b/drivers/dma/cppi41.c
index ddd4a3932127e0d9e1343d6cd5f1c17eb2068ac9..cf119a8ccdd5fd6bb861f2b83c47731b9873bc51 100644 (file)
--- a/drivers/dma/cppi41.c
+++ b/drivers/dma/cppi41.c
@@ -585,9 +585,22 @@ 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) {
@@ -610,7 +623,13 @@ 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)