Re: [PATCH v2 03/10] i2c: xiic: Switch to Xiic standard mode for i2c-read

[Marek Vasut]

On 6/29/22 16:09, Krzysztof Adamski wrote:
> Hi Marek,
>
> W dniu 29.06.2022 o 16:05, Marek Vasut pisze:
> > > [...]
> > >
> > > If those two modes only differ in software complexity but we are not
> > > able to support only the simpler one and we have support for the more
> > > complicated (standard mode) anyways, we know that standard mode
> > > can handle or the cases while dynamic mode cannot, we also know that
> > > dynamic mode is broken on some versions of the core, why do we actually
> > > keep support for dynamic mode?
> >
> > If I recall it right, the dynamic mode was supposed to handle 
> > transfers longer than 255 Bytes, which the core cannot do in Standard 
> > mode. It is needed e.g. by Atmel MXT touch controller. I spent a lot 
> > of time debugging the race conditions in the XIIC, which I ultimately 
> > fixed (the patches are upstream), but the long transfers I rather 
> > fixed in the MXT driver instead.
> >
> > I also recall there was supposed to be some update for the XIIC core 
> > coming with newer vivado, but I might be wrong about that.
>
> It seems to be the other way around - dynamic mode is limited to 255 
> bytes - when you trigger dynamic mode you first write the address of the 
> slave to the FIFO, then you write the length as one byte so you can't 
> request more than 255 bytes. So *standard* mode is used for those 
> messages. In other words - dynamic mode is the one that is more limited 
> - everything that you can do in dynamic mode you can also do in standard 
> mode. So why don't we use standard mode always for everything?

Sigh, it's been a year since I looked into this, sorry.

One of the modes is maybe not supported on all the XIIC core instances ?