linux-kernel - Re: [PATCH] Topcliff PHUB: Generate PacketHub driver

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Message-Id: <201006081129.48362.arnd@arndb.de>
Date:	Tue, 8 Jun 2010 11:29:48 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Masayuki Ohtake" <masa-korg@....okisemi.com>
Cc:	"LKML" <linux-kernel@...r.kernel.org>,
	"Andrew" <andrew.chih.howe.khor@...el.com>,
	"Intel OTC" <joel.clark@...el.com>, "Wang, Qi" <qi.wang@...el.com>,
	"Wang, Yong Y" <yong.y.wang@...el.com>
Subject: Re: [PATCH] Topcliff PHUB: Generate PacketHub driver

On Tuesday 08 June 2010, Masayuki Ohtake wrote:
> We are studying your indication.
> > My feeling is that this ioctl interface is too
> > low-level in general. You only export access to specific
> > registers, not to functionality exposed by them.
> > The best kernel interfaces are defined in a way that
> > is independent of the underlying hardware and
> > convert generic commands into device specific commands.
> 
> I have a question.
> We don't know 'generic commands' concretely.
> Let me know 'generic commands' in detail.

I have not seen the application using the driver, but
a better abstraction IMHO would be to take an abstraction
you have in your application and move it into the kernel.

I can be more specific if you tell me where to find the
source of the application. Generally speaking, you'd
transform a function like

/* the function that knows how to do 'this' */
int phub_do_this(int phub_fd, unsigned long arg)
{
	struct pch_phub_req req = {
		.addr_offset = SOME_ADDR_OFF,
	};
	ioctl(fd, IOCTL_PHUB_READ_REG, &req);

	if (req.data & SOME_BITS)
		return ERROR;

	req.addr_offset = ANOTHER_ADDR_OFF;
	req.data = arg | REALLY_DO_IT_BITMASK;

	ioctl(fd, IOCTL_PHUB_WRITE_REG, &req);

	return 0;
}

into another function that does the same thing but
without knowing anything about the registers:

/* the same function on the abstract interface */
int phub_do_this_new(int phub_fd, unsigned long arg)
{
	return ioctl(phub_fd, IOCTL_PHUB_DO_THIS, &arg);
}

	Arnd
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