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

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Date:   Mon, 11 Feb 2019 11:42:24 +0100
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Vishal Sagar <vishal.sagar@...inx.com>, hyun.kwon@...inx.com,
        laurent.pinchart@...asonboard.com, mchehab@...nel.org,
        robh+dt@...nel.org, mark.rutland@....com, michals@...inx.com,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        sakari.ailus@...ux.intel.com, hans.verkuil@...co.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        dineshk@...inx.com, sandipk@...inx.com
Subject: Re: [PATCH v3 2/2] media: v4l: xilinx: Add Xilinx MIPI CSI-2 Rx
 Subsystem

Hi Vishal,

On 01/02/19 13:56, Vishal Sagar wrote:
> The Xilinx MIPI CSI-2 Rx Subsystem soft IP is used to capture images
> from MIPI CSI-2 camera sensors and output AXI4-Stream video data ready
> for image processing. Please refer to PG232 for details.

For those unused to Xilinx documentation I'd use the full document name
("MIPI CSI-2 Receiver Subsystem v4.0") or, even better, a stable URL if
available.

> The driver is used to set the number of active lanes, if enabled
> in hardware. The CSI2 Rx controller filters out all packets except for
> the packets with data type fixed in hardware. RAW8 packets are always
> allowed to pass through.
> 
> It is also used to setup and handle interrupts and enable the core. It
> logs all the events in respective counters between streaming on and off.
> The generic short packets received are notified to application via
> v4l2_events.
> 
> The driver supports only the video format bridge enabled configuration.
> Some data types like YUV 422 10bpc, RAW16, RAW20 are supported when the
> CSI v2.0 feature is enabled in design. When the VCX feature is enabled,
> the maximum number of virtual channels becomes 16 from 4.
> 
> Signed-off-by: Vishal Sagar <vishal.sagar@...inx.com>

...

> +/**
> + * xcsi2rxss_reset - Does a soft reset of the MIPI CSI2 Rx Subsystem
> + * @core: Core Xilinx CSI2 Rx Subsystem structure pointer
> + *
> + * Core takes less than 100 video clock cycles to reset.
> + * So a larger timeout value is chosen for margin.
> + *
> + * Return: 0 - on success OR -ETIME if reset times out
> + */
> +static int xcsi2rxss_reset(struct xcsi2rxss_core *core)
> +{
> +	u32 timeout = XCSI_TIMEOUT_VAL;

The comment about the timeout is duplicated here and at the #define
line. Why not removing the define above and just putting

  u32 timeout = 1000; /* us */

here? It would make the entire timeout logic appear in a unique place.

> +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)?

> +	return ret;
> +}


-- 
Luca