Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find dma channel

["Måns Rullgård" <mans@mansr.com>]

Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:

> On Tue, 2015-12-15 at 23:34 +0000, Måns Rullgård wrote:
>> Mans Rullgard <mans@mansr.com> writes:
>> 
>> > Currently this driver only works with a DesignWare DMA engine which
>> > it
>> > registers manually using the second "reg" address range and
>> > interrupt
>> > number from the DT node.
>> > 
>> > This patch makes the driver instead use the "dmas" property if
>> > present,
>> > otherwise optionally falling back on the old way so existing device
>> > trees can continue to work.
>> > 
>> > With this change, there is no longer any reason to depend on the
>> > 460EX
>> > machine type so drop that from Kconfig.
>> > 
>> > Signed-off-by: Mans Rullgard <mans@mansr.com>
>> > ---
>> >  drivers/ata/Kconfig          |  10 ++-
>> >  drivers/ata/sata_dwc_460ex.c | 192 +++++++++++++++++++++++++++--
>> > --------------
>> >  2 files changed, 131 insertions(+), 71 deletions(-)
>> 
>> The corresponding patch for the canyonlands devicetree looks
>> something
>> like this.  I don't have any such hardware or even a manual, so I
>> don't
>> know what values to use for the various required DT properties of the
>> DMA controller node, nor can I test it.  The SATA driver works with a
>> different DMA controller on a Sigma Designs chip.
>> 
>> diff --git a/arch/powerpc/boot/dts/canyonlands.dts
>> b/arch/powerpc/boot/dts/canyonlands.dts
>> index 3dc75de..959f36e 100644
>> --- a/arch/powerpc/boot/dts/canyonlands.dts
>> +++ b/arch/powerpc/boot/dts/canyonlands.dts
>> @@ -190,12 +190,22 @@
>>  					 /* DMA */ 0x2 &UIC0 0xc
>> 0x4>;
>>  		};
>>  
>> +		DMA0: dma@bffd0800 {
>> +			compatible = "snps,dma-spear1340";
>> +			reg = <4 0xbffd0800 0x400>;
>> +			interrupt-parent = <&UIC3>;
>> +			interrupts = <0x5 0x4>;
>> +			#dma-cells = <3>;
>> +			/* required properties here */
>
> You have to move the master assignments and other custom dw_dmac
> properties. Maybe at some point I will fix that in dw/platform.c.
>
>> +		};

The current sata_dwc driver calls dw_dma_probe() with null pdata which
causes the dw_dma driver to auto-detect most parameters.  It looks like
simply omitting those properties here results in the same thing,
although in this case dw_dma_parse_dt() leaves a devm-allocated pdata
struct adrift.  Deferring the allocation of that and changing the DT
binding doc to make these properties optional for auto-detect-capable
hardware should just work.  Something like this:

diff --git a/drivers/dma/dw/platform.c b/drivers/dma/dw/platform.c
index 68a4815..f90c465 100644
--- a/drivers/dma/dw/platform.c
+++ b/drivers/dma/dw/platform.c
@@ -103,18 +103,21 @@ dw_dma_parse_dt(struct platform_device *pdev)
 	struct device_node *np = pdev->dev.of_node;
 	struct dw_dma_platform_data *pdata;
 	u32 tmp, arr[DW_DMA_MAX_NR_MASTERS];
+	u32 nr_channels;
 
 	if (!np) {
 		dev_err(&pdev->dev, "Missing DT data\n");
 		return NULL;
 	}
 
+	if (of_property_read_u32(np, "dma-channels", nr_channels))
+		return NULL;
+
 	pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
 	if (!pdata)
 		return NULL;
 
-	if (of_property_read_u32(np, "dma-channels", &pdata->nr_channels))
-		return NULL;
+	pdata->nr_channels = nr_channels;
 
 	if (of_property_read_bool(np, "is_private"))
 		pdata->is_private = true;


-- 
Måns Rullgård