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

From: [email-masked] (Martin Sperl)
Date: Thu, 14 Jan 2016 09:48:56 +0100

On 14.01.2016 05:07, Vinod Koul wrote:
> On Wed, Jan 13, 2016 at 03:24:59PM +0100, Martin Sperl wrote:
>>>> But that would be frowned upon, so I had to come up with the approach
>>>> taken, which makes the following assumptions:
>>>
>>> DT was designed to move this info and hardcoding from kernel into
>>> DT, so why cant we do that?
>> We still need to be backwards-compatible - at least that is what
>> everyone tells me, so I need to hard-code fallbacks for those values.
>
> IMO hard code for falling back is okay as that supports old cases and new
> platforms use geric DT info and new devices can be supported generically,
> please check with DT folks..
>
>>>> * the DT maps only the interrupts that are assigned to the HW block
>>>> * the driver knows about the number of DMA channels in HW
>> that could be a DT property, yes.
>>>> * the driver knows about the mapping of shared interrupts
>>>>    (11-14 share irq).
>> OK - how would you define that "mapping" in a "sane" manner in the DT
>> that allows us to have multiple such mappings in the future?
>
> You are hard coding the flags for each channel, we can pass this for each
> channel in the interrupt configi, a flag share/none..? Please run this thru
> DT experts and I am not one of them..
>
>>>> 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.
>>>
>>> I still think DT is the right way to go here, unless I hear some other
>>> convincing answer..
>>>
>>
>> The point is that the way the DT is right now it becomes very hard to
>> extend it in a sane manner - It would be bitmaps/lists here,
>> bitmaps/lists there...
>>
>> Breaking the DT would make all of it go away.
>>
>> If I think of it (reading your other comments), then here how the
>> "new" DT could look like:
>> dma: dma at 7e007f00 {
>> 	/* new compatible name to map to new driver */
>> 	compatible = "brcm,bcm2835-dma-v2";
>>
>> 	/* the status/enable registers */
>> 	reg = <0x7e007f00 0x100>;
>>
>> 	/* the catch all interrupt */
>> 	interrupts = <1 28>;
>>
>> 	dma0: dma-channel at 0x7e007000 {
>> 		reg = <0x7e007000 0x100>;
>> 		interrupts = <1 16>;
>> 	};
>> 	...
>> 	dma7: dma-channel at 0x7e007700 {
>> 		reg = <0x7e007700 0x100>;
>> 		interrupts = <1 23>;
>> 		dma-channel-type = <BCM2835_DMA_LITE>;
>> 		dma-max-length = <65532>; /* 64K - 4 */
>> 	};
>> 	...
>> 	dma11: dma-channel at 0x7e007b00 {
>> 		reg = <0x7e007b00 0x100>;
>> 		interrupts = <1 27>;
>> 		shared-interrupt;
>> 		dma-channel-type = <BCM2835_DMA_LITE>;
>> 	};
>> 	...
>> 	dma14: dma-channel at 0x7e007e00 {
>> 		reg = <0x7e007e00 0x100>;
>> 		interrupts = <1 27>;
>> 		shared-interrupt;
>> 		dma-channel-type = <BCM2835_DMA_LITE>;
>> 	};
>> 	dma15: dma-channel at 0x7ee05000 {
>> 		reg = <0x7ee05000 0x100>;
>> 	};
>> };
>
> This looks okay to me to start with...

Can we please agree on something over the next 2 weeks, so that I can
implement it when I get back from vacation?

The point is that it would be a much more explicit device-tree
with the way I had proposed it above.

I guess we still could use the same driver (compatiblity)
with some reorganization. To detect old and new DTs we could
just check the size of regs or number of interrupts and if they
are reg.len > 256 bytes or count(interrupts) = 13  then fall back
to legacy probe...

Thanks,
	Martin