linux-kernel - Re: Question about UIO vs DT

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Message-ID: <2025051549-flannels-lively-a46d@gregkh>
Date: Thu, 15 May 2025 09:52:29 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc: Linux-Kernel <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org,
	shimoda <yoshihiro.shimoda.uh@...esas.com>,
	goda <yusuke.goda.sx@...esas.com>,
	Kurokawa <harunobu.kurokawa.dn@...esas.com>,
	Kihara <takeshi.kihara.df@...esas.com>,
	kazuya.mizuguchi.ks@...esas.com, takamitsu.honda.pv@...esas.com
Subject: Re: Question about UIO vs DT

On Thu, May 15, 2025 at 04:45:23AM +0000, Kuninori Morimoto wrote:
> 
> Hi Greg / UIO / DT
> 
> I would like to ask about UIO vs DT.
> 
> If my understanding was correct, current UIO can use 1 IRQ / 1 reg per 1 UIO,
> but some device needs multi-IRQ/reg. In such case, we need to use
> multi-UIO. But it is not good much to DT rule. For example in case of
> the device which needs "2 regs 3 irqs". it will be
> 
> (A)	[1 reg, 1 IRQ] UIO
> (B)	[1 reg, 1 IRQ] UIO
> (C)	[0 reg, 1 IRQ] UIO
> 
> and (C) will be DT error. Is this known issue ? Do we have better solution ?

Yes, write a real driver for the device as obviously it is a complex one
and UIO shouldn't be used for it :)

What type of device is this that requires this type of hardware control
and why do you feel that UIO is the proper solution?

thanks,

greg k-h