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.
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