Device Tree formatting for multiple virtual channels in ti-vpe/cal driver?

* Device Tree formatting for multiple virtual channels in ti-vpe/cal driver?
@ 2017-02-10  9:34 Thomas Axelsson
  2017-02-12 22:16 ` Sakari Ailus
  0 siblings, 1 reply; 3+ messages in thread
From: Thomas Axelsson @ 2017-02-10  9:34 UTC (permalink / raw)
  To: linux-media

Hi,

I have a TI AM571x CPU, and I'm trying to add support for multiple MIPI CSI-2 
virtual channels per PHY (port) to the ti-vpe/cal.c driver (CAMSS/CAL peripheral,  
ch. 8 in Datasheet [1]). This CPU can have more contexts (virtual channels) per PHY 
than what it has DMA handlers. Each PHY may have up to 8 contexts, and there are 2 
PHYs, but there are only 8 DMA channels in total. It is not required to use DMA to 
receive data from the context.

Since it will be very useful to specify which contexts will use DMA and which will 
not, the proper place to do this seems to be the device tree.

This becomes rather messy though, since it needs to be specified in the device tree 
node pointed to by the remote-endpoint field - yet, it's decided by the capabilities 
of the master component (in this case the CAL), so the remote-endpoint is a weird 
place to put it.

I have made an example [2] using the Device Tree example in 
Documentation/devicetree/bindings/media/ti-cal.txt (my own comments).
In the ar0330_1 endpoint, I have:
* Put multiple virtual channels in "reg", as in 
  Documentation/devicetree/bindings/mipi/dsi/mipi-dsi-bus.txt,
* Added "dma-write" for specifying which virtual channels should get written 
  directly to memory through DMA,
* Added "vip" just to show that a Virtual Channel can go somewhere else than 
  through DMA write.
* Added "pix-proc" to show that pixel processing might be applied to some of the 
  Virtual Channels.

What is your advice on how to properly move forward with adding support like this?

Thank you in advance.

Best regards,
Thomas Axelsson

[1] http://www.ti.com/lit/gpn/am5716

[2]
--------------------------------------------------
cal: cal@4845b000 {
    compatible = "ti,dra72-cal";
    ti,hwmods = "cal";

    /* snip */

    ports {
        #address-cells = <1>;
        #size-cells = <0>;
        csi2_0: port@0 {
            reg = <0>;                         /* PHY index, must match port index */
            status = "okay";                   /* Enable */
            endpoint {
                slave-mode;
                remote-endpoint = <&ar0330_1>;
            };
        };
        csi2_1: port@1 {
            reg = <1>;                         /* PHY Index */
        };
    };
};

i2c5: i2c@4807c000 {
    ar0330@10 {
        compatible = "ti,ar0330";
        reg = <0x10>;
        port {
            #address-cells = <1>;
            #size-cells = <0>;
            ar0330_1: endpoint {
                reg = <0 1 2>;                 /* Virtual Channels */
                dma-write = <0 2>;             /* Virtual Channels that will use 
                                                  Write DMA */
                vip = <1>;                     /* Virtual Channel to send on to 
                                                  Video Input Port */
                pix-proc = <2>;                /* Virtual channels to apply pixel
                                                  processing on */
                clock-lanes = <1>;             /* Clock lane indices */
                data-lanes = <0 2 3 4>;        /* Data lane indices */
                remote-endpoint = <&csi2_0>;
            };
        };
    };
};
--------------------------------------------------

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