Re: [RFC v2 2/2] dt-bindings: mipi-dsi: Add dual-channel DSI related info
From: Andrzej Hajda <hidden>
Date: 2018-06-07 10:39:03
Also in:
dri-devel, linux-arm-msm
On 07.06.2018 01:08, Heiko Stuebner wrote:
Am Mittwoch, 6. Juni 2018, 18:07:46 CEST schrieb Archit Taneja:quoted
On Wednesday 06 June 2018 04:16 PM, Heiko Stübner wrote:quoted
Hi Archit, Am Mittwoch, 6. Juni 2018, 12:21:16 CEST schrieb Archit Taneja:quoted
On Wednesday 06 June 2018 02:00 PM, Heiko Stübner wrote:quoted
Am Mittwoch, 6. Juni 2018, 07:59:29 CEST schrieb Archit Taneja:quoted
On Monday 04 June 2018 05:47 PM, Heiko Stuebner wrote:quoted
Am Donnerstag, 18. Januar 2018, 05:53:55 CEST schrieb Archit Taneja:quoted
Add binding info for peripherals that support dual-channel DSI. Add corresponding optional bindings for DSI host controllers that may be configured in this mode. Add an example of an I2C controlled device operating in dual-channel DSI mode. Signed-off-by: Archit Taneja <redacted>Looks like a great solution for that problem, so Reviewed-by: Heiko Stuebner <heiko@sntech.de> As I'm looking into that for my rk3399-scarlet device right now and couldn't find this patchset in the kernel yet, is it planned to merge or refresh these binding changes or were problems encountered. At least an Ack/Review from Rob seems to be missing.I forgot about these patches. Rob had reviewed the first one in the set the second one still needed an Ack. I'll post a v3 that adds the Reviewed-bys and fixes a small typo.very nice ... because it looks like yesterday I managed to make the Rockchip dsi work in dual mode following this. But one question came up, do you really want two input ports on the panel side? I.e. hardware-wise, I guess the panel will have one 8-lane or so input thatonly gets split up on the soc side onto 2 dsi controllers?I think all dual DSI panels actually have 2 DSI controllers/parsers within them, one on each port. The MIPI DSI spec doesn't support 8 lanes. Also, the pixels coming out of the host are distributed among the lanes differently than what would have been the case with a 'theoretical' 8 lane receiver. Other than that, some dual DSI panels only accept DSI commands on the 'master' port, where as others expect the same command to be sent across both the ports. Therefore, I think it's better to represent dual DSI panels having 2 DSI input ports. Your DT looks good to me.Hmm, that doesn't match up then ;-) ... as my dt uses 2 endpoints in one port for the dsi-links.Sorry, I didn't notice you'd created two endpoints within a single port. I don't think I'm particular about 2 ports vs 1 port with 2 endpoints. They both seem okay to me as long as we follow it consistently. I'm myself not 100% sure of how to figure where one should prefer endpoints over ports. Maybe someone more familiar with the of graph bindings could comment here.
Port should describe physical port, endpoint are used to describe multiple links to the same port. If the panel has two physical DSI interfaces it should use two ports.
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The issue I see with using ports and not endpoints for dual-dsi links is with distinguishing between input and output ports. For a panel that's easy, as you every port will be an input port and if you have 2, it's supposed dual-dsi. But for example I guess there might exist some dual-dsi-to-something bridges, where you would end up with say 3 (or even more) ports ... two dual-dsi inputs and 1 or more outputs.Okay, I get your point here. Although, even if the remote device had exactly 2 ports. Is it safe to assume that port #0 is an input port and port #1 is an output port? Is that the norm?I don't think that anything like that is specified anywhere, so you cannot assume anything about what a port contains.
Ports are defined per device-node and port number assignment should be described in particular device bindings. So device driver knows well which functions should be assigned to which port. But it is private matter of the device/device driver. Different device bindings can assign different number for input and output ports, but since ports are private thing for devices it should not be a problem. I do not see why do you have such issue, could you describe it more.
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I've at least seen one device (toshiba,tc358767 bridge) that can actually take either DPI as input or DSI based on how you configure it. There are 2 input ports here, port #0 for DSI and port #1 for DPI. Would it have made sense here to have a single port and 2 endpoints here too?Nope, I guess having a port for DPI input, one port for DSI input makes quite a lot of sense. And then you can have the input-specifics living in the endpoints like dual links or so.quoted
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While the following argument might not be 100% valid from a dt-purity standpoint implementing this might get hairy for _any_ operating system, as you will need each panel/bridge to tell what the ports are used for.Yeah.
Each panel/bridge should know what his ports are used for, but to who and why you want to communicate it?
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I.e. in my endpoint based mapping, right now I have this nice and generic WIP function to parse the of_graph and get the master+slave nodes: https://github.com/mmind/linux-rockchip/blob/tmp/rk3399-gru-bob-scarlet/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c#L697 [0]I'd tried out something locally before posting this patch, I don't have the code for it, but I can describe the steps I took. This code expects the panel/bridge to have 2 input ports.Which again would be very much panel-specific as you cannot assume to much about the ports.quoted
1. DSI0 host driver looks up its output port, gets the remote endpoint, and get this endpoint's parent (using of_graph_get_remote_port_parent()). Keeps the parent device node in a temp variable. 2. DSI1 host driver does the same thing. 3. DSI0 and DSI1 check whether their outputs are connected to the same device. If so, they're in dual DSI mode. If not, they are operating independently. The positive of this approach is that we don't need to make any assumptions about the panel/bridge's port numbers, which is great. The negative is that our DSI controller instances now need to query each other, which can be messy, but not too hard to implement.
I think detection of dual dsi and whole configuration thing of dual-dsi should be done using in-kernel frameworks (maybe new ones :) ). Could you describe necessary configuration steps to be performed, what info should be passed from who to who, etc. It would be easier to discuss. Anyway I think there are rules which probably we should always (almost) obey: 1. one port per interface, if it is control port it could be probably omitted. 2. device drivers should only look into their private nodes, nodes pointed by remote-endpoints should be used only/mainly for identification of in-kernel objects exposed by in-kernel frameworks. Regards Andrzej
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I think the choice finally boils down to what makes more sense w.r.t representing the HW correctly. We'd need Rob's comment on that.Taking your DPI+DSI example from above actually shows quite nicely how ports+endpoints could play together. panel-or-bridge@0 { compatible = "something,something"; reg = <0>; ports { /* DPI input */ port@0 { endpoint { remote-endpoint = <&dpi_out>; }; }; /* DSI input */ port@1 { /* from first dsi controller */ endpoint@0 { remote-endpoint = <&dsi0_out>; }; /* from second dsi controller */ endpoint@1 { remote-endpoint = <&dsi1_out>; }; }; /* another input, or an output for a bridge */ port@2 { endpoint { remote-endpoint = <&somewhere>; } }; }; }; But yeah, hopefully we can entice Rob for comments :-) . Heikoquoted
Thanks, Architquoted
So I guess my proposal would be to have one port for inputs and one port for outputs for dsi peripherals, with possibly multiple endpoints in each. Heiko [0] github seems to have reliability problems, so for reference my parsing function: static int dw_mipi_dsi_is_dual(struct dw_mipi_dsi_rockchip *dsi, struct device_node **master, struct device_node **slave) { struct device_node *local_ep, *remote_port, *ep; struct device_node *ctrls[2] = { NULL, NULL }; int num = 0, ret = 0, idx; /* get local panel endpoint of the dsi controller */ local_ep = of_graph_get_endpoint_by_regs(dsi->dev->of_node, 1, 0); if (!local_ep) { DRM_DEV_ERROR(dsi->dev, "couldn't find local panel endpoint\n"); return -ENXIO; } /* get panel port */ remote_port = of_graph_get_remote_port_parent(local_ep); of_node_put(local_ep); if (!remote_port) { DRM_DEV_ERROR(dsi->dev, "couldn't find panel port\n"); return -ENXIO; } /* check other endpoints */ for_each_endpoint_of_node(remote_port, ep) { struct device_node *np = of_graph_get_remote_port_parent(ep); if (!np) continue; idx = of_property_read_bool(np, "clock-master"); /* * Either master or slave already defined, drop refcnt * but catch errors only after the full loop. */ if (ctrls[idx]) of_node_put(np); else ctrls[idx] = np; num++; } of_node_put(remote_port); if (num > 2) { DRM_DEV_ERROR(dsi->dev, "too many dsi devices linked\n"); ret = -EINVAL; goto cleanup; } /* nothing to do */ if (num < 1) { ret = 0; goto cleanup; } if (!ctrls[1]) { DRM_DEV_ERROR(dsi->dev, "no master defined in dual-dsi\n"); ret = -ENODEV; goto cleanup; } if (!ctrls[0]) { DRM_DEV_ERROR(dsi->dev, "no slave defined in dual-dsi\n"); ret = -ENODEV; goto cleanup; } *master = ctrls[1]; *slave = ctrls[0]; return 1; cleanup: for (idx = 0; idx < 2; idx++) if (ctrls[idx]) of_node_put(ctrls[idx]); return ret; }quoted
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So right now I'm operating with a devicetree like &mipi_dsi { status = "okay"; clock-master; ports { mipi_out: port@1 { reg = <1>; mipi_out_panel: endpoint { remote-endpoint = <&mipi_in_panel>; }; }; }; mipi_panel: panel@0 { compatible = "innolux,p097pfg"; reg = <0>; backlight = <&backlight>; enable-gpios = <&gpio4 25 GPIO_ACTIVE_HIGH>; pinctrl-names = "default"; pinctrl-0 = <&display_rst_l>; port { #address-cells = <1>; #size-cells = <0>; mipi_in_panel: endpoint@0 { reg = <0>; remote-endpoint = <&mipi_out_panel>; }; mipi1_in_panel: endpoint@1 { reg = <1>; remote-endpoint = <&mipi1_out_panel>; }; }; }; }; &mipi_dsi1 { status = "okay"; ports { mipi1_out: port@1 { reg = <1>; mipi1_out_panel: endpoint { remote-endpoint = <&mipi1_in_panel>; }; }; }; }; I guess it is a matter of preference on what reflects the hardware best, so maybe that's Robs call? Heikoquoted
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--- v2: - Specify that clock-master is a boolean property. - Drop/add unit-address and #*-cells where applicable. .../devicetree/bindings/display/mipi-dsi-bus.txt | 80 ++++++++++++++++++++++ 1 file changed, 80 insertions(+)diff --git a/Documentation/devicetree/bindings/display/mipi-dsi-bus.txtb/Documentation/devicetree/bindings/display/mipi-dsi-bus.txt index 94fb72cb916f..7a3abbedb3fa 100644--- a/Documentation/devicetree/bindings/display/mipi-dsi-bus.txt +++ b/Documentation/devicetree/bindings/display/mipi-dsi-bus.txt@@ -29,6 +29,13 @@ Required properties: - #size-cells: Should be 0. There are cases where it makes sense to use a different value here. See below. +Optional properties: +- clock-master: boolean. Should be enabled if the host is being usedin + conjunction with another DSI host to drive the same peripheral. Hardware + supporting such a configuration generally requires the data on both the busses + to be driven by the same clock. Only the DSI host instance controlling this + clock should contain this property. + DSI peripheral ==============@@ -62,6 +69,16 @@ primary control bus, but are also connected to a DSIbus (mostly for the data>> path). Connections between such peripherals and a DSI host can be represented using the graph bindings [1], [2]. +Peripherals that support dual channel DSI +----------------------------------------- + +Peripherals with higher bandwidth requirements can be connected to 2 DSI +busses. Each DSI bus/channel drives some portion of the pixel data (generally +left/right half of each line of the display, or even/odd lines of the display). +The graph bindings should be used to represent the multiple DSI busses that are +connected to this peripheral. Each DSI host's output endpoint can be linked to +an input endpoint of the DSI peripheral. + [1] Documentation/devicetree/bindings/graph.txt [2] Documentation/devicetree/bindings/media/video-interfaces.txt@@ -71,6 +88,8 @@ Examples with different virtual channel configurations. - (4) is an example of a peripheral on a I2C control bus connected with to a DSI host using of-graph bindings. +- (5) is an example of 2 DSI hosts driving a dual-channel DSIperipheral, + which uses I2C as its primary control bus. 1) dsi-host {@@ -153,3 +172,64 @@ Examples }; }; }; + +5) + i2c-host { + dsi-bridge@35 { + compatible = "..."; + reg = <0x35>; + + ports { + #address-cells = <1>; + #size-cells = <0>; + + port@0 { + reg = <0>; + dsi0_in: endpoint { + remote-endpoint = <&dsi0_out>; + }; + }; + + port@1 { + reg = <1>; + dsi1_in: endpoint { + remote-endpoint = <&dsi1_out>; + }; + }; + }; + }; + }; + + dsi0-host { + ... + + /* + * this DSI instance drives the clock for both the host + * controllers + */ + clock-master; + + ports { + ... + + port { + dsi0_out: endpoint { + remote-endpoint = <&dsi0_in>; + }; + }; + }; + }; + + dsi1-host { + ... + + ports { + ... + + port { + dsi1_out: endpoint { + remote-endpoint = <&dsi1_in>; + }; + }; + }; + };-- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html-- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html_______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
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