Re: [Gumstix-users] Gpio event example

[Norman T. <nlt...@gm...>]

Now that we are talking about using the Overo ISP, and custom camera modules:

I'd like to comment on that last point; the generation of a V4L2
driver (vs., let us say, passing the address of the video memory
storage to the application, and other means of kernel/app
communication such as signals). What are the benefits of creating it
as a V4L2 driver, the deficits, and the benefits of using a different
method instead? I'd like to hear from other people who developed these
kernel modules for cameras or similar devices.

Norman Tuttle

On Wed, Nov 10, 2010 at 2:53 PM, Bertho Stultiens <be...@va...> wrote:
> On 11/10/2010 04:15 PM, Norman Tuttle wrote:
> [snip]
>> By
>> setting this up as an LKM, which carefully manages its resources both
>> when installing and uninstalling the module, we can easily make
>> modifications and still avoid recompiling the entire kernel or even
>> having to reboot the system to test changes (just inserting and
>> deleting the LKM from the system as needed).
>
> Using an LKM is the right method because resources are properly tracked,
> assuming your module is doing it right. And, yes, there is a very steep
> learning curve. And on top of the learning curve you have the
> continually evolving interfaces in the kernel, which you should/need to
> track and adopt.
>
>
>> There is probably an art to knowing exactly which programming should
>> be done inside and outside the kernel, and I am learning and
>> hopefully improving that art.
> [snip]
>
> As long as you do not need the timing or access to interrupts, you can
> do most things from userspace and should actually do so from userspace.
> That is, until you trample on shared resources. The interface boundary
> is normally about abstractions and generalizations.
>
> Per your example, a custom camera module, you should have a v4l2 driver.
> That would automatically mean that all/most existing userspace apps can
> be used.
>
>
> --
> Greetings Bertho
>
> (disclaimers are disclaimed)
>
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