Using atmel-isi for direct output on framebuffer ?

From the AT91 datasheet, I understand that the ISI interface is capable

Hello Josh,

I am currently looking at V4L2 and your atmel-isi driver for an AT91 based platform on which I would like the ISI interface to capture the image from a camera and have this image directly output in RGB format at a specific location on the screen (so that it can be nicely integrated into a Qt application for example).

At the moment, I grab frames from the V4L2 device to userspace, do the YUV -> RGB conversion manually in my application, and then displays the converted frame on the framebuffer thanks to normal Qt painting mechanisms. This works, but obviously consumes a lot of CPU.

Quoted 1 line

From the AT91 datasheet, I understand that the ISI interface is capable

of doing the YUV -> RGB conversion and is also capable of outputting the frame at some location in the framebuffer, but I don't see how to use this capability with the Linux V4L2 and framebuffer infrastructures.

Is this possible ? If so, could you provide some pointers or starting points to get me started ? If not, what is missing in the driver ?

Thanks a lot,

Thomas

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Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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Hello Josh,

I am currently looking at V4L2 and your atmel-isi driver for an AT91 based platform on which I would like the ISI interface to capture the image from a camera and have this image directly output in RGB format at a specific location on the screen (so that it can be nicely integrated into a Qt application for example).

At the moment, I grab frames from the V4L2 device to userspace, do the YUV -> RGB conversion manually in my application, and then displays the converted frame on the framebuffer thanks to normal Qt painting mechanisms. This works, but obviously consumes a lot of CPU.

From the AT91 datasheet, I understand that the ISI interface is capable of doing the YUV -> RGB conversion and is also capable of outputting the frame at some location in the framebuffer, but I don't see how to use this capability with the Linux V4L2 and framebuffer infrastructures.

Is this possible ? If so, could you provide some pointers or starting points to get me started ? If not, what is missing in the driver ?

Thanks a lot,

Thomas

Signature · 8 lines

Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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To unsubscribe from this list: send the line "unsubscribe linux-media" in
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My understanding is that you want to use Atmel ISI to output RGB data then work with framebuffer. So yes, it is possible.

Since current atmel_isi.c only uses its codec path to output YUV data. So first need add RGB format support in isi_camera_get_formats(). Then you have two choices to enable RGB output of ISI: 1. Enable isi's preview path(DMA, interrupts) to convert YUV to RGB. 2. Or still use codec path but don't need add much ISI code, just set camera sensor(if it support RGB565 output) to output RGB565 data for ISI, then what the data ISI output now should be RGB565 format. But in this way you cannot do any scale.

For V4L2_CAP_VIDEO_OVERLAY type driver, I don't know much about that.

Doing the YUV -> RGB within the V4L2 driver is something I understand quite well. The part I miss is how the V4L2 driver interacts with the framebuffer driver to output the camera image into the framebuffer.

Quoted 1 line

For V4L2_CAP_VIDEO_OVERLAY type driver, I don't know much about that.

Hum, ok, found http://v4l2spec.bytesex.org/spec/x6570.htm which seems to explain a bit the userspace interface for this.

Quoted 2 lines · Josh

My understanding is that you want to use Atmel ISI to output RGB data then work with framebuffer. So yes, it is possible.

Good.

Quoted 8 lines

Since current atmel_isi.c only uses its codec path to output YUV data. So first need add RGB format support in isi_camera_get_formats(). Then you have two choices to enable RGB output of ISI: 1. Enable isi's preview path(DMA, interrupts) to convert YUV to RGB. 2. Or still use codec path but don't need add much ISI code, just set camera sensor(if it support RGB565 output) to output RGB565 data for ISI, then what the data ISI output now should be RGB565 format. But in this way you cannot do any scale.

Doing the YUV -> RGB within the V4L2 driver is something I understand quite well. The part I miss is how the V4L2 driver interacts with the framebuffer driver to output the camera image into the framebuffer.

Quoted 1 line

For V4L2_CAP_VIDEO_OVERLAY type driver, I don't know much about that.

Hum, ok, found http://v4l2spec.bytesex.org/spec/x6570.htm which seems to explain a bit the userspace interface for this.

I'm not sure if V4L2_CAP_VIDEO_OVERLAY is a good solution for this. This driver type (or rather buffer type) was used on old systems to capture directly to the PCI graphics card memory. Nowadays I would advice using USERPTR with framebuffer memory.

Quoted 4 lines · Laurent Pinchart

I'm not sure if V4L2_CAP_VIDEO_OVERLAY is a good solution for this. This driver type (or rather buffer type) was used on old systems to capture directly to the PCI graphics card memory. Nowadays I would advice using USERPTR with framebuffer memory.

Could you give a short summary of how the USERPTR mechanism works?