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SubjectRe: [PATCH 2/2] New driver: Xillybus generic interface for FPGA (programmable logic)
On Sun, Dec 02, 2012 at 07:26:27PM +0200, Eli Billauer wrote:
> On 11/30/2012 06:32 PM, Greg KH wrote:
> >>>>> >>+static struct class *xillybus_class;
> >>>> >Why not just use the misc interface instead of your own class?
> >>> When Xillybus is used, the whole system's mission is usually around
> >>> it (e.g. it's a computer doing data acquisition through the Xillybus
> >>> pipes). So giving it a high profile makes sense, I believe. Besides,
> >>> a dozen of device files are not rare.
> >It is no problem to create dozens of misc devices. It makes your driver
> >smaller, contain less code that I have to audit and you have to ensure
> >you got right, and it removes another user of 'struct class' which we
> >are trying to get rid of anyway. So please, move to use a misc device.
> >
>
> It has just occurred to me that DYNAMIC_MINORS is 64
> (drivers/char/misc.c), so I guess that limits the number of misc
> devices that can be generated, at least with dynamically allocated
> minors. I previously mentioned "a dozen" as the number of devices,
> but I've already run tests with 100+ devices, and I can also think
> of a sane application for that.
>
>
> So if I understood the situation correctly, it looks like using misc
> devices will create a limitation which will be reached sooner or
> later.
>
> Any suggestion what to do?

Given that I don't really understand how you can have that many device
nodes, because I don't know what they all seem to be needed for, I can't
answer this question.

Again, any hints on the user/kernel api you use/need here? Does it
really have to be device nodes? What's wrong with the simple firmware
interface the kernel provides?

thanks,

greg k-h


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