[PATCH V2 3/8] dmaengine: bcm2835: use shared interrupt for channel 11 to 14.

[Martin Sperl]

On 13.01.2016 13:26, Vinod Koul wrote:
> On Thu, Jan 07, 2016 at 05:33:01PM +0000, kernel at martin.sperl.org wrote:
>> @@ -638,13 +666,21 @@ static int bcm2835_dma_probe(struct platform_device *pdev)
>>   		goto err_no_dma;
>>   	}
>>
>> -	for (i = 0; i < pdev->num_resources; i++) {
>> -		irq = platform_get_irq(pdev, i);
>> +	for (i = 0; i <= BCM2835_DMA_MAX_CHANNEL_NUMBER; i++) {
>> +		if (BCM2835_DMA_IRQ_SHARED_MASK & BIT(i)) {
>
> Ideally this should be done thru DT data and not hard coded in kernel. I
> dont think this assumption will hold good for next gen of this device, so
> better to get this from DT!

The ideal solution would be breaking the DT in such a way that we could
define a register range and interrupt per dma-channel looking something
like this:

diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
index 83d9787..9526b91 100644
--- a/arch/arm/boot/dts/bcm2835.dtsi
+++ b/arch/arm/boot/dts/bcm2835.dtsi
@@ -31,8 +31,28 @@

                 dma: dma at 7e007000 {
                         compatible = "brcm,bcm2835-dma";
-                       reg = <0x7e007000 0xf00>;
-                       interrupts = <1 16>,
+                       reg = <0x7e007f00 0x100>, /* status reg */
+                             /* dma channel 0-14 base addresses */
+                             <0x7e007000 0x100>,
+                             <0x7e007100 0x100>,
+                             <0x7e007200 0x100>,
+                             <0x7e007300 0x100>,
+                             <0x7e007400 0x100>,
+                             <0x7e007500 0x100>,
+                             <0x7e007600 0x100>,
+                             <0x7e007700 0x100>,
+                             <0x7e007800 0x100>,
+                             <0x7e007900 0x100>,
+                             <0x7e007a00 0x100>,
+                             <0x7e007b00 0x100>,
+                             <0x7e007c00 0x100>,
+                             <0x7e007d00 0x100>,
+                             <0x7e007e00 0x100>,
+                             /* dma channel 15 uses a different base */
+                             <0x7ee05000 0x100>;
+                       interrupts = <1 28>, /* catch all DMA-interrupts */
+                                    /* dma channel 0-10 interrupts */
+                                    <1 16>,
                                      <1 17>,
                                      <1 18>,
                                      <1 19>,
@@ -43,9 +63,30 @@
                                      <1 24>,
                                      <1 25>,
                                      <1 26>,
+                                    /* dma channel 11-14 share irq */
                                      <1 27>,
-                                    <1 28>;
-
+                                    <1 27>,
+                                    <1 27>,
+                                    <1 27>,
+                                    /* no irq support for dma channel 15 */
+                                    < 0 >;
+                       dma-names = "shared",
+                                   "dma0",
+                                   "dma1",
+                                   "dma2",
+                                   "dma3",
+                                   "dma4",
+                                   "dma5",
+                                   "dma6",
+                                   "dma7",
+                                   "dma8",
+                                   "dma9",
+                                   "dma10",
+                                   "dma11",
+                                   "dma12",
+                                   "dma13",
+                                   "dma14",
+                                   "dma15";
                         #dma-cells = <1>;
                         brcm,dma-channel-mask = <0x7f35>;
(or similar)

This actually would allow us to make "brcm,dma-channel-mask" redundant,
as we could remove those dma channels that are owned by the firmware
directly from the list.

That way we could also map other capabilities via the DT.

It would also allow a transparent addition of additional dma channels
with newer versions of the HW - mostly - by modifying the DT.

But that would be frowned upon, so I had to come up with the approach
taken, which makes the following assumptions:
* the DT maps only the interrupts that are assigned to the HW block
* the driver knows about the number of DMA channels in HW
* the driver knows about the mapping of shared interrupts
   (11-14 share irq).

It is not optimal, but at least it works with the least amount of
change to the DT - and what about all those assumptions that we
would need to hard-code to be backwards compatible to the DT without?

I guess we could replace BCM2835_DMA_MAX_CHANNEL_NUMBER with:
   /* we do not support dma channel 15 with this driver */
   #define BCM2835_DMA_MAX_CHANNEL_SUPPORTED 14
   ...
   for (i = 0;
        i <= min_t(int, flv(chans_available), 
BCM2835_DMA_MAX_CHANNEL_SUPPORTED);
        i++) {

So which way would you prefer this to go - I got another few days
before I leave on vacation.

Thanks,
	Martin