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

From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
To: Tony Lindgren <tony@atomide.com>,
	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>,
	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: Re: [PATCH] dmaengine: cppi41: Fix cppi41_dma_prep_slave_sg() when idle
Date: Wed, 23 Oct 2019 21:55:40 +0300	[thread overview]
Message-ID: <6996a5de-215b-f9a2-1aeb-5eeed1b7cf8d@cogentembedded.com> (raw)
In-Reply-To: <20191023153138.23442-1-tony@atomide.com>

Hello!

On 10/23/2019 06:31 PM, Tony Lindgren wrote:

> 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) {

   I'd call that variable 'status', comparison (error < 0) just doesn't look right.
If it was *if* (error), it would have been more correct. 

> +		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) {
[...]

MBR, Sergei