linux-kernel - Re: [PATCH 0/4] drivers/misc: add rawio framework and drivers

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Date:	Tue, 22 Oct 2013 10:14:00 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Bin Gao <bin.gao@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] drivers/misc: add rawio framework and drivers

On Tue, Oct 22, 2013 at 06:44:06AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Oct 21, 2013 at 05:03:17PM -0700, Bin Gao wrote:
> > To read/write registers from a device is very important on embedded system,
> > especially SoC systems. Physically there could be different types of devices
> > based on bus tyes, e.g. PCI devices, I2C (slave)devices, I/O devices(memory
> > mapped), inter-processor devices, etc. Typically there are userland
> > tools from
> > PC Linux to access device registers, but on some embedded system initrd and
> > rootfs come with a minimal busybox and most useful userland tools are not
> > available. To add these tools back to rootfs is not convenient either.
> > What's more, on some systems with runtime pm enabled, reading/writing
> > registers
> > from a device which is in low power state will cause problems. For these
> > reasons, to have some tools/interfaces directly from kernel space via debug
> > fs seems to be easy, cheap and convenient.
> 
> So, just because userspace is "hard" you want to add stuff to the kernel
> instead.
> 
> Sorry, but for over the past decade, we have been doing just the
> opposite, if things can be done in userspace, then they should be done
> there.  So for us to go in the opposite direction, like these patches
> show, would be a major change.
> 
> > These patchsets are designed to  achieve above goals to ease
> > device driver and kernel debugging on embedded systems.
> > 
> > Rawio provides a framework to read/write registers from a bus, including
> > pci, i2c, I/O device(memory mapped), etc. based on debug fs.
> > Rawio bus drivers implement the read/write operation on a specific bus
> > on top of the rawio framework driver.
> > Currently only three bus drivers are available: pci, iomem and i2c.
> 
> You can already do this today for PCI with the UIO framework, right?
> Why duplicate that functionality here with another userapce API that we
> will then have to maintain for the next 40+ years?
> 
Same for i2c, where the same functionality is supported through i2c-tools and
the i2c-dev driver. Adding i2c-tools to initramfs and/or to the root file system
should not be that much of an issue, much less than having to maintain two APIs
for the same purpose.

Guenter
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