linux-kernel - Re: [PATCH v3 2/2] media: v4l: xilinx: Add Xilinx MIPI CSI-2 Rx Subsystem

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Message-ID: <7fc3bd7b-4537-3df5-12ee-55ebec17a8bd@lucaceresoli.net>
Date:   Mon, 11 Feb 2019 15:30:47 +0100
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Vishal Sagar <vsagar@...inx.com>,
        Vishal Sagar <vishal.sagar@...inx.com>,
        Hyun Kwon <hyunk@...inx.com>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Michal Simek <michals@...inx.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
        "hans.verkuil@...co.com" <hans.verkuil@...co.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dinesh Kumar <dineshk@...inx.com>,
        Sandip Kothari <sandipk@...inx.com>
Subject: Re: [PATCH v3 2/2] media: v4l: xilinx: Add Xilinx MIPI CSI-2 Rx
 Subsystem

Hi,

thanks for the quick reply.

On 11/02/19 13:43, Vishal Sagar wrote:
>>> +static int xcsi2rxss_start_stream(struct xcsi2rxss_state *state)
>>> +{
>>> +     struct xcsi2rxss_core *core = &state->core;
>>> +     int ret = 0;
>>> +
>>> +     xcsi2rxss_enable(core);
>>> +
>>> +     ret = xcsi2rxss_reset(core);
>>> +     if (ret < 0) {
>>> +             state->streaming = false;
>>> +             return ret;
>>> +     }
>>> +
>>> +     xcsi2rxss_intr_enable(core);
>>> +     state->streaming = true;
>>
>> Shouldn't you propagate s_stream to the upstream subdev here calling
>> v4l2_subdev_call(..., ..., s_stream, 1)?
>>
> 
> This is done by the xvip_pipeline_start_stop() in xilinx-dma.c for Xilinx Video pipeline.

Indeed it does, however other CSI2 RX drivers do propagate s_stream in
their own s_stream. Not strictly related to this driver, but what's the
logic for having these two different behaviors?

Also xvip_pipeline_start_stop() only follows the graph through
entity->pads[0], so it looks like it cannot handle entities with
multiple sink pads. How would it be able to handle e.g. the AXI4-Stream
Switch [0], which has 2+ sink pads?

[0]
https://www.xilinx.com/support/documentation/ip_documentation/axis_infrastructure_ip_suite/v1_1/pg085-axi4stream-infrastructure.pdf
(page 16).

-- 
Luca