spi: dw: Add deferred DMA-channels setup support

Currently if the source DMA device isn't ready to provide the channels
capable of the SPI DMA transfers, the DW SSI controller will be registered
with no DMA support. It isn't right since all what the driver needs to do
is to postpone the probe procedure until the DMA device is ready. Let's
fix that in the framework of the DWC SSI generic DMA implementation. First
we need to use the dma_request_chan() method instead of the
dma_request_slave_channel() function, because the later one is deprecated
and most importantly doesn't return the failure cause but the
NULL-pointer. Second we need to stop the DW SSI controller probe procedure
if the -EPROBE_DEFER error is returned on the DMA initialization. The
procedure will resume later when the channels are ready to be requested.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
---
 drivers/spi/spi-dw-core.c |  5 ++++-
 drivers/spi/spi-dw-dma.c  | 25 ++++++++++++++++++-------
 2 files changed, 22 insertions(+), 8 deletions(-)

On Fri, Jun 10, 2022 at 02:22:28PM +0300, Andy Shevchenko wrote:
> On Fri, Jun 10, 2022 at 10:50:06AM +0300, Serge Semin wrote:
> > Currently if the source DMA device isn't ready to provide the channels
> > capable of the SPI DMA transfers, the DW SSI controller will be registered
> > with no DMA support. It isn't right since all what the driver needs to do
> > is to postpone the probe procedure until the DMA device is ready. Let's
> > fix that in the framework of the DWC SSI generic DMA implementation. First
> > we need to use the dma_request_chan() method instead of the
> > dma_request_slave_channel() function, because the later one is deprecated
> > and most importantly doesn't return the failure cause but the
> > NULL-pointer. Second we need to stop the DW SSI controller probe procedure
> > if the -EPROBE_DEFER error is returned on the DMA initialization. The
> > procedure will resume later when the channels are ready to be requested.
> 

> One nit-pick below
> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

Thanks.

> 
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > ---
> >  drivers/spi/spi-dw-core.c |  5 ++++-
> >  drivers/spi/spi-dw-dma.c  | 25 ++++++++++++++++++-------
> >  2 files changed, 22 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
> > index ecea471ff42c..911ea9bddbee 100644
> > --- a/drivers/spi/spi-dw-core.c
> > +++ b/drivers/spi/spi-dw-core.c
> > @@ -942,7 +942,9 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
> >  
> >  	if (dws->dma_ops && dws->dma_ops->dma_init) {
> >  		ret = dws->dma_ops->dma_init(dev, dws);
> > -		if (ret) {
> > +		if (ret == -EPROBE_DEFER) {
> > +			goto err_free_irq;
> > +		} else if (ret) {
> >  			dev_warn(dev, "DMA init failed\n");
> >  		} else {
> >  			master->can_dma = dws->dma_ops->can_dma;
> > @@ -963,6 +965,7 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
> >  	if (dws->dma_ops && dws->dma_ops->dma_exit)
> >  		dws->dma_ops->dma_exit(dws);
> >  	dw_spi_enable_chip(dws, 0);
> > +err_free_irq:
> >  	free_irq(dws->irq, master);
> >  err_free_master:
> >  	spi_controller_put(master);
> > diff --git a/drivers/spi/spi-dw-dma.c b/drivers/spi/spi-dw-dma.c
> > index 63e5260100ec..1322b8cce5b7 100644
> > --- a/drivers/spi/spi-dw-dma.c
> > +++ b/drivers/spi/spi-dw-dma.c
> > @@ -139,15 +139,20 @@ static int dw_spi_dma_init_mfld(struct device *dev, struct dw_spi *dws)
> >  
> >  static int dw_spi_dma_init_generic(struct device *dev, struct dw_spi *dws)
> >  {
> > -	dws->rxchan = dma_request_slave_channel(dev, "rx");
> > -	if (!dws->rxchan)
> > -		return -ENODEV;
> > +	int ret;
> >  
> > -	dws->txchan = dma_request_slave_channel(dev, "tx");
> > -	if (!dws->txchan) {
> > -		dma_release_channel(dws->rxchan);
> > +	dws->rxchan = dma_request_chan(dev, "rx");
> > +	if (IS_ERR(dws->rxchan)) {
> > +		ret = PTR_ERR(dws->rxchan);
> >  		dws->rxchan = NULL;
> 
> > -		return -ENODEV;
> > +		goto err_exit;
> 

> This change doesn't bring anything...

Right, but it makes this method looking alike dw_spi_dma_init_mfld().
I even used the same label names. It makes the code a little bit easier
to read.

> 
> > +	}
> > +
> > +	dws->txchan = dma_request_chan(dev, "tx");
> > +	if (IS_ERR(dws->txchan)) {
> > +		ret = PTR_ERR(dws->txchan);
> > +		dws->txchan = NULL;
> > +		goto free_rxchan;
> >  	}
> >  
> >  	dws->master->dma_rx = dws->rxchan;
> > @@ -160,6 +165,12 @@ static int dw_spi_dma_init_generic(struct device *dev, struct dw_spi *dws)
> >  	dw_spi_dma_sg_burst_init(dws);
> >  
> >  	return 0;
> > +
> > +free_rxchan:
> > +	dma_release_channel(dws->rxchan);
> > +	dws->rxchan = NULL;
> 
> > +err_exit:
> 

> ...and this too.

ditto

-Sergey

> 
> > +	return ret;
> >  }
> >  
> >  static void dw_spi_dma_exit(struct dw_spi *dws)
> > -- 
> > 2.35.1
> > 
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>