Inheriting from Mmio class

[Johannes Schlatow]

Hey Martin,

looks great. I also had in mind that the generic part from Mmio should be separated as Mmio is already a specialisation of IO access.

So, how do we proceed. Do you want to do the refactoring yourself and I add the I2c implementation afterwards?

Cheers
 Johannes

On Fri, 9 Dec 2016 09:42:04 +0100
Martin Stein <martin.stein at ...1...> wrote:

> Hey Johannes,
> 
> I could not get it out of my mind. What do you think of the following
> solution scheme:
> 
> ~~~util/io_space.h~~~
> 
> template <typename IO>
> class Io_space
> {
> 	..
> 	public:
> 
> 		Io_space(IO &io) ..
> 
> 		template .. struct Register ..;
> 		template .. struct Register_array ..;
> 	
> 		template .. read(..)  { .. _io._read(..); .. }
> 		template .. write(..) { .. _io._write(..); .. }
> 		..
> };
> 
> ~~~util/mmio.h~~~
> 
> class Mmio : public Io_space<Mmio>
> {
> 	friend class Io_space<Mmio>;
> 
> 	private:
> 
> 		template .. _read(..)  { .. }
> 		template .. _write(..) { .. }
> 
> 	public:
> 
> 		Mmio_b(addr_t base) : Io_space<Mmio_accessor>(*this) ..
> };
> 
> ~~~i2c_io.h~~~
> 
> class I2c_io : public Io_space<I2c_io> { .. };
> 
> ~~~~~~
> 
> This would keep the back-end hidden and enable diversification.
> 
> Cheers,
> Martin
> 
> Am 08.12.2016 um 15:37 schrieb Martin Stein:
> > Hi Johannes,
> > 
> > We actually had an internal discussion about such an approach. As far as
> > I remember, it was in the context of the Zynq drivers. I absolutely like
> > the idea of using the Mmio framework with different back-ends. I think
> > you would have to exchange merely the two raw-access methods of the
> > framework:
> > 
> > ! template <typename _ACCESS_T>
> > ! void Mmio::_write(off_t const, _ACCESS_T const)'
> > !
> > ! template <typename _ACCESS_T>
> > ! _ACCESS_T Mmio::_read(off_t const) const
> > 
> > The read<>() and write<>() methods you mention should not contain any
> > code that depends on the way of accessing registers but only the bit and
> > offset logic that could be reused.
> > 
> > I'm curious about the outcome of your idea and help willingly if you
> > have further questions.
> > 
> > Cheers,
> > Martin
> > 
> > Am 07.12.2016 um 18:26 schrieb Johannes Schlatow:  
> >> Hi,
> >>
> >> I really like Genode's Register API as it makes accessing memory mapped hardware registers quite clean and simple.
> >>
> >> However, I recently encountered the need to access a rather complex I2C slave device. The I2C controller itself is accessible via MMIO. Yet, the slave device itself has a notion of registers. Basically, you first send the register address to the I2C slave and, in a second transaction, you can read/write the register's value.
> >>
> >> Being used to the clean appearance of MMIO in Genode, I was wondering whether the access to I2C slave registers could be wrapped in a similar way. My intuition is that it might simply suffice to inherit from the Mmio class and modify the write<>() and read<>() functions but haven't checked the code in detail. Any suggestions/ideas?
> >>
> >> Cheers
> >>  Johannes
> >>
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-- 
Johannes Schlatow, M.Sc.

IDA, Institute of Computer and Network Engineering
Technische Universität Braunschweig
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