Hi all I've been re-thinking (yes, again...) our classical 2-step geometry configuration (let's leave COMPOSE and friends aside for now) per S_FMT and S_CROP, and came to the conclusion, that passing the pixel format with the scaling configuration (S_FMT) is a bad idea.
Let's take CAPTURE as an example, and let's use the "sensor" terminology, even though the same basically applies to other video data sources. Considering just the two geometries - a cropped window on the sensor and an output frame, it is logical to first configure the input, and then the output, because at least on the hardware, where you have to write scaling factors into registers, and not just output sizes, you would have to recalculate those factors, if cropping were to be applied after scaling. In other words, output depends on the input, but not the other way round:-) But S_FMT also passes the pixel format with it, and if you change the pixel format, your cropping capabilities might change too. This might not be very obvious for raw sensors, but it is quite possible for various video data processing devices, like resizers, etc. Therefore, I think, the best order would be: (1) set pixel format (fourcc / mediabus code) (2) set crop (3) set scale I know we cannot change this in V4L2 anymore, so, this might be something for V4L3;-) But what we could do is at least redesign our subdevice APIs to separate the .s_fmt() method into two operations. Below is the specific example, that brought me to this, it might be helpful for those, wishing to even better understand the sources of this problem, others can skip the rest:-) The problem occurred to me, when I was working on the sh_mobile_ceu_camera.c driver. The CEU can scale some pixel formats (several YUV / NV1x formats), and cannot scale others (this actually holds for all bridges), but it can crop anything. As I'm extending soc-camera to work in both "V4L2" and "MC" modes, I want to still be able to configure the sensor behind the CEU from just the classical S_FMT / S_CROP ioctl()s. In this mode I have to decide, where to do the cropping and scaling - on the sensor or on the CEU. One thing I want to avoid, is applying CEU cropping on top of sensor scaling - this gets messy very quickly. So, I only consider CEU cropping, when the sensor is not scaling. Given this, if the user has requested one of pixel codes, that the CEU cannot scale (e.g., a Bayer format), and I have configured sensor 1:1 scaling and crop on the CEU, and then the user issues an S_FMT, I now also lose the ability to ask the sensor to scale, because for that I would have to drop the CEU cropping and the resulting cropping rectangle can change _a lot_ as a result of an S_FMT ioctl(), which, as we know, is not something, that the user expects;-) This leads me to the conclusion, that I also should not do CEU cropping for those, not natively supported by the CEU, formats. This is where we come to cropping behaviour depending on the pixel format and the need to set that format before cropping and before scaling. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
