[U-Boot] [PATCH] 0/12 Multiadapter/multibus I2C

[ksi at koi8.net]

On Sat, 14 Feb 2009, Heiko Schocher wrote:

> Hello ksi,
> 
> ksi at koi8.net wrote:
> > On Fri, 13 Feb 2009, Heiko Schocher wrote:
> >> ksi at koi8.net wrote:
> >>> Here is the second attempt for initial portion of multibus/multiadapter
> >>> I2C support.
> >>>   
> >> Can you please send your patches with some better commit messages.
> >> You only send your Signed-off-by, without any explanation. Please
> >> change this.
> > 
> > There is not much sense in extensive commit messages in this case, IMHO. It
> > is not a bug fix or added feature at one particular place; it is a major
> > rework. The only message I can give is something like "Changes for
> > multiadapter/multibus I2C support..."
> > 
> > I'll add it to the second attempt that I will make later today.
> > 
> >>> This includes a set of common files, all drivers in drivers/i2c and all
> >>> boards affected by these changes (config files, board files, and lib_xx
> >>> files.)
> >>>
> >>> There is an illustrative example of multiadapter multibus I2C config in
> >>> MPC8548CDS.h config file (#if 0'd.) Definitions in that example are
> >>> bogus so please don't expect it to work. It will compile though...
> >>>
> >>> This set also includes big rework for soft_i2c.c that makes it template
> >>> version that allows up to 4 bitbanged adapters. This number can be
> >>>   
> >> Didn;t you try my suggestion? This is a really big define monster now,
> >> which I think, we can avoid, and without to change nearly all lines of
> >> the existing driver.
> > 
> > We can not avoid it. At least I can not see an easy way to do this. SOFT_I2C
> 
> Yes, we can. Look again deeper in my approach, this _is_ an easy way!
> 
> I also looked again in your changes in the fsl_i2c.c driver, and we
> can make this also simplier, by using cur_adap_nr->hwadapnr!

OK, please explain how that cur_adap_nr->hwadapnr gets assigned. Please also
explain how can one invoke a function on other adapter than "current".
Remember, i2c_init is quite often called BEFORE the code is relocated to RAM
so you can NOT change "current" adapter.

Please also note that you will loose a capability of working with more than
one adapter before the code is relocated to RAM.

> We have not to define for both hardware adapter each function in
> i2c_adap_t! For example:
> 
> You did:
> static void fsl_i2c1_init(int speed, int slaveadd)
> {
> 	__i2c_init(0, speed, slaveadd);
> }
> 
> instead we only need
> 
> i2c_init(cur_adap_nr->hwadapnr, speed, slaveadd);
> 
> with
> 
> i2c_adap_t	fsl_i2c_adap[] = {
> 	{
> 		.init		=	i2c_init,
> [...]
> 		.hwadapnr	=	0,
> 		.name		=	FSL_NAME(CONFIG_SYS_FSL_I2C_OFFSET)
> 	},
> #ifdef CONFIG_SYS_FSL_I2C2_OFFSET
> 	{
> 		.init		=	i2c_init,
> [...]
> 		.hwadapnr	=	1,
> 		.name		=	FSL_NAME(CONFIG_SYS_FSL_I2C2_OFFSET)
> 	},
> #endif

It would've been easy if we had had "this" pointer. That would allow us to
find out what adapter we are running on by using something like
"this->hwadapnr." Unfortunately we do NOT have such a pointer, we're plain
C. Function in a structure does not have a way to find out how to access a
member of that structure. The only way to somehow find which "hwadapnr" we
are running at is using a global variable, cur_i2c_bus as a starting point.
But that is meaningless until the code is relocated to RAM and that variable
became writable. And that robs us of added possibility of using any adapter
other than a single one preset in config file before relocating to RAM.

That is if we want to keep the original I2C API. The other, simpler way is
to add an argument to each and every function, a pointer to i2c_adap_t
structure or its index or something similar. But that defeats the entire
purpose of this code by requiring to find and change each and every call to
any I2C function in the entire U-Boot source thus totally breaking ALL
existing code 99.99% of which only use single I2C adapter/bus...

> Please change this driver also!

I can't. Please read above.

> If I think more, we never even need to change the function parameters
> like you did for example for i2c_int ()! We can use at the beginning
> of every function who go in i2c_adap_t, the "cur_adap_nr->hwadapnr"
> and make the settings we need for this function... and wow we saved
> one function parameter.

Devil is in the details... Please read above.

> > is special. Those multiple e.g. MXC or OMAP3 adapters can be parameterized
> > because different channels do only differ in their base address that can be
> > made into a parameter. Software I2C is totally different because it has
> 
> Why is this different? If you change a base or the way to the pins?

Because the pins on different channels can be accessesed in absolutely
different way.

> > totally different functions for different channels, there is nothing we can
> 
> Think about my explanation to the soft_i2c.c driver in previous EMail and
> above function.
> 
> It also works!

Partially and with handicaps. Please read my reply to that message.

> > make into a parameter. All those I2C_SDA etc. are NOT DEFINES, they are
> > MACROS. Every function for every channel is built of those macros that can
> 
> I know this in your approach, but we _don;t_ need this. We simply can make
> one "common" board function and switch in this function dependent on the
> "cur_adap_nr->hwadapnr" to the particular GPIO pin functions, wherever the
> are!

Please read above.

> > be absolutely different for each channel. They define NOT some PARAMETERS
> > but function TEXT that will be compiled into executable code.
> 
> And this additional TEXT I save too!

You don't save anything. And you add complexity and break uniformity. BTW,
what is a reason to save on text?

> I think, you think too much in C++?

No, I'm not a C++ guy. I prefer assembly and only use C where it is
absolutely necessary :) I do not program in C++/Java/etc. at all and only
know C++ basics and a bit of other stuff required to fix occasional bugs in
other people's code.

It is not C++, it is common sence and good engineering practices. And I'm an
engineer first and only then a programmer, a machinist, an electronic
engineer, a gunsmith and so on.

> > This is how it is done in Linux kernel (see e.g. drivers/hwmon/lm93.c.)
> 
> Thats no argument.

Sure it is not. This is a suggestion.

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