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| Who | What | When |
|---|---|---|
| koike | sailus, Hi. in the v4l2_subdev_link_validate function, if you can't get the format, 0 is returned, I would like to check why with you (as you are the author of the code) because I am implementing my own link_validate function and I would like to know if I should return 0 as well. Thank you | [23:21] |
| *** | hverkuil_ changes his alias to hverkuil | [10:50] |
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| headless_ changes his alias to headless | [12:00] | |
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| pinchartl | hverkuil: it still bothers me a bit. I was wondering whether we couldn't add a flag to struct v4l2_ext_control instead. when set for G_EXT_CTRLS it would indicate that the default value should be read, and when set for S_EXT_CTRLS it would indicate that the user wants to set the control to its default value
that would avoid adding a new ioctl and would allow setting a control to its default value without having to read it first I also liked Sakari's proposal of extending the query control ioctl instead of adding a new ioctl but I agree it makes it a bit more difficult for userspace to reset a control to its default value not much though what bothers me is that we treat the default value in a specific way, even though it's already reported by the query control ioctl one of the benefits of the new proposed ioctl is that it would allow getting the default value of multiple controls in a single call if we think that's important, wouldn't it make sense to instead create a new query control ioctl that could query multiple controls in a single go, without restricting that to just the default value ? | [12:15] |
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| hverkuil | pinchartl: it's the fact that you can get the default values and set them with just two ioctls that is so nice. Even with a query_ext_ctrls ioctl you still cannot do that.
Using a flag instead of a new ioctl is something I thought about, but I'd have to take one of the only two reserved fields in struct v4l2_ext_controls. It's also something that only applies to getting values, never for try/set. | [13:43] |
| pinchartl | yes, the lack of reserved fields is something that bothers me too
they're scarse resources the flag could apply to set though, as I've explained above applications could use it to set a control to its default value without having to read it first the value would be ignored when the flag is set don't we have a single reserved field in v4l2_ext_controls, not two ? | [13:49] |
| hverkuil | v4l2_ext_controls has two, v4l2_ext_control has one. | [13:52] |
| pinchartl | yes, my bad
I was thinking about adding the flag to v4l2_ext_control | [13:53] |
| hverkuil | It's just ugly. You get exceptions: if the flag is set, then use the default value. But what does that mean for the union? Do you still have to allocate it? And it's tricky in v4l2-ctrls as well. | [13:54] |
| pinchartl | my concern is that I feel we're really special-casing this while it could be more generic, and I bet it will bite us back when we'll get to the next similar-by-slightly-different use case
I've described the various ideas I had to make this a bit more generic but none of them are clearly better and 100fb6158erfect so I won't nack the proposed approach, but I still feel we could do better (back in 15 minutes) | [13:55] |
| hverkuil | One option might be to create a V4L2_CTRL_CLASS_DEFAULTS control class that can be used in the ctrl_class field. It's only supported (at least for now) by G_EXT_CTRLS.
it still feels a bit like a hack, but at least it does allow it to be extended to e.g. CLASS_MIN, MAX, STEP should we ever want that. | [14:04] |
| pinchartl | hmmmm...
a bit hackish indeed I need to go shopping from groceries before the store closes I'll be back a bit later | [14:11] |
| hverkuil | ctrl_class should really be renamed to 'which'
0 = current values existing control classes == 'current values for those control classes' (only needed for backwards compat) V4L2_CTRL_WHICH_DEFAULTS == default control values and with the request patch series (per frame configuration) you'd get 'control values for the given request ID' trying to use WHICH_DEFAULTS with S/TRY_EXT_CTRLS would naturally return EACCES since the default control values are read-only. | [14:13] |
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| *** | demhlyr changes his alias to demhlyr_
demhlyr_ changes his alias to demhlyr9 demhlyr9 changes his alias to demhlyr | [18:54] |
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| sailus | koike: Getting the format should only fail if the driver doesn't implement the op. We haven't had a case where that'd happen yet, so I don't think it's a very important question as such.
However if the entity type is wrong, that's indeed a more serious problem. This apparently isn't handled properly at the moment. But to answer your question, I think I'd return zero if you simply can't get the format for a pad. | [21:10] |
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| koike | sailus, thank you for your answer. I think I'll return error, as all the subdevices in my topology should implement the get format ops | [22:49] |
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