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Date:	Fri, 25 Jul 2014 12:19:02 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Kweh Hock Leong <hock.leong.kweh@...el.com>,
	Eric Miao <eric.y.miao@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Chew Chiau Ee <chiau.ee.chew@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>, chiauee85@...il.com,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH] spi/pxa2xx-pci: Enable DMA binding through device name

On Friday 25 July 2014 12:55:59 Mika Westerberg wrote:
> On Fri, Jul 25, 2014 at 12:07:14PM +0300, Mika Westerberg wrote:
> > On Fri, Jul 25, 2014 at 10:38:36AM +0200, Arnd Bergmann wrote:
> > > On Friday 25 July 2014 11:22:49 Mika Westerberg wrote:
> > > > > All you need to do is change your filter function to take the
> > > > > slave id from pxa_spi_info and stick it in there, e.g.
> > > > > 
> > > > > static bool pxa2xx_spi_dw_dma_filter(struct dma_chan *chan, void *param)
> > > > > {       
> > > > >         const struct pxa2xx_spi_master *pdata = param;
> > > > >         struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
> > > > >         
> > > > >         dwc->request_line = fargs->req;
> > > > >         dwc->src_master = 0;
> > > > >         dwc->dst_master = 0;
> > > > >         
> > > > >         return 1;
> > > > > }           
> > > > 
> > > > Oh man. That makes pxa2xx_spi dependent on a certain specific DMA engine
> > > > driver.
> > > 
> > > I think you can improve this by putting the filter function (and a pointer
> > > to it) into the pxa2xx_spi_master data provided by the PCI driver.
> > 
> > Indeed, that looks better. It still makes the PCI part of the driver
> > dependent on a particular DMA engine driver but is certainly better than
> > the core pxa2xx_spi driver.
> 
> Something like this?
> 
> Hock Leong / Chiaue Ee, are you able to check if this works on your BYT
> machines?

I think I found a small bug, and one detail that could be improved.

> @@ -321,12 +310,14 @@ int pxa2xx_spi_dma_setup(struct driver_data *drv_data)
>  		return -ENOMEM;
>  
>  	drv_data->tx_chan = dma_request_slave_channel_compat(mask,
> -				pxa2xx_spi_dma_filter, pdata, dev, "tx");
> +				pdata->dma_filter, pdata->dma_filter_param,
> +				dev, "tx");
>  	if (!drv_data->tx_chan)
>  		return -ENODEV;

If you change this part to pass '(void *)info->tx_slave_id' rather than
pdata->dma_filter_param, you can simplify the next code:

> +static bool pxa2xx_spi_pci_dma_filter(struct dma_chan *chan, void *param)
> +{
> +	struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
> +	const struct pxa_spi_info *info = param;
> +
> +	if (chan->chan_id == info->tx_chan_id)
> +		dwc->request_line = info->tx_slave_id;
> +	else if (chan->chan_id == info->rx_chan_id)
> +		dwc->request_line = info->rx_slave_id;
> +	else
> +		return false;
> +
> +	dwc->src_master = 0;
> +	dwc->dst_master = 0;
> +
> +	return true;
> +}

to disregard the tx_chan_id, which is really arbitrary as far as I can tell.

What I think you got wrong here (by following my bad advice) is the master
number. Looking at the code for dw_dma, I think src_master needs to be '1'
for your driver.

If we do the same change in the drivers/tty/serial/8250/8250_pci.c driver,
the dw_dma driver can be simplified a little by removing the special
case for the request line setting.

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 1af731b83b3f..674f69fe6662 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -37,24 +37,6 @@
  * support descriptor writeback.
  */
 
-static inline bool is_request_line_unset(struct dw_dma_chan *dwc)
-{
-	return dwc->request_line == (typeof(dwc->request_line))~0;
-}
-
-static inline void dwc_set_masters(struct dw_dma_chan *dwc)
-{
-	struct dw_dma *dw = to_dw_dma(dwc->chan.device);
-	struct dw_dma_slave *dws = dwc->chan.private;
-	unsigned char mmax = dw->nr_masters - 1;
-
-	if (!is_request_line_unset(dwc))
-		return;
-
-	dwc->src_master = min_t(unsigned char, mmax, dwc_get_sms(dws));
-	dwc->dst_master = min_t(unsigned char, mmax, dwc_get_dms(dws));
-}
-
 #define DWC_DEFAULT_CTLLO(_chan) ({				\
 		struct dw_dma_chan *_dwc = to_dw_dma_chan(_chan);	\
 		struct dma_slave_config	*_sconfig = &_dwc->dma_sconfig;	\
@@ -967,10 +949,6 @@ set_runtime_config(struct dma_chan *chan, struct dma_slave_config *sconfig)
 	memcpy(&dwc->dma_sconfig, sconfig, sizeof(*sconfig));
 	dwc->direction = sconfig->direction;
 
-	/* Take the request line from slave_id member */
-	if (is_request_line_unset(dwc))
-		dwc->request_line = sconfig->slave_id;
-
 	convert_burst(&dwc->dma_sconfig.src_maxburst);
 	convert_burst(&dwc->dma_sconfig.dst_maxburst);
 
@@ -1123,8 +1101,6 @@ static int dwc_alloc_chan_resources(struct dma_chan *chan)
 	 * doesn't mean what you think it means), and status writeback.
 	 */
 
-	dwc_set_masters(dwc);
-
 	spin_lock_irqsave(&dwc->lock, flags);
 	i = dwc->descs_allocated;
 	while (dwc->descs_allocated < NR_DESCS_PER_CHANNEL) {

	Arnd
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