Re: i.MX8M Nano ISI Channel Question

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Adam,

(CC'ing Frank Li)

On Thu, Apr 24, 2025 at 08:59:18PM -0500, Adam Ford wrote:
> NXP-
> 
> I am trying use Libcamera to capture video on an i.MX8M Nano.
> (Hopefully, this makes Laurent smile)
> 
> I noticed that it has a maximum capture of 1080 lines when I query it
> with Libcamera, but the same camera on the Mini can capture at higher
> rates.  The multimedia overview states it can handle 1 unprocessed
> camera stream at 4kp30 without scaling.  The Nano's Ref manual later
> states that each processing channel has one line buffer, and each line
> buffer can store up to 2048 pixels.  It continues to describe when
> processing higher resolution images like 4k, the line buffer from
> other channels can be combined.
> 
> Section 13.4.3.5 of the Nano's Ref manual (Rev 2, dated 07/2022)
> explicitly goes into detail on how to capture up to 4k image
> resolution by combining channel 'n' with channel 'n+1' which implies
> there are at least two channels.
> 
> Section 13.4.5.1 states the registers are dedicated for each channel
> and spaced 64KB apart, but then the following table only shows the
> base address for one, and Table 2-6 shows the ISI size is 64KB.
> 
> The driver is currently written to only support 1 channel.  When
> reading through the driver, it appears to require one IRQ per channel,
> so I looked through the Nano's IRQ table (7-1), and found there are
> three:
> ISI Camera Channel 0 Interrupt - 16
> ISI Camera Channel 1 Interrupt - 42
> ISI Camera Channel 2 Interrupt - 43
> 
> I attempted to enable a second channel by modifying the .num_channels
> = 2 value in the driver, and I modified my device tree to assign a
> second IRQ (42), but when I query the pipeline with libcamera, it
> still doesn't show an available resolution ov 2592x1944 that is
> supported by the camera and work on the Mini without the ISI system.
> 
> Can someone tell me how many channels are actually available, and
> whether or not  4Kp30 video is really available on the Nano?

My understanding, based on the i.MX8MN reference manual, is that the ISI
has a single channel. The ISI features list (13.4.1.2) reports

• Supports up to 2K resolution at 30 or 60 fps (24bpp) on each channel.

If you look at the i.MX8MP reference manual, the same features list
reports

• Supports one source of 4K resolution at 30 fps (24bpp).
• Supports up to 2K resolution at 30 or 60 fps (24bpp) on each channel.

There's no mention of 4K in the i.MX8MN ISI features. I expect that the
documentation about 4K support by combining pixel buffers comes from the
generic ISI documentation, and is not applicable to the i.MX8MN.

-- 
Regards,

Laurent Pinchart