Re: [PATCH v6 1/3] serial: sh-sci: Add OF support

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Bastian,

On Thursday 07 March 2013 11:26:29 Bastian Hecht wrote:
> Hi Laurent,
> 
> >> +- renesas,scscr : Should contain a bitfield used by the Serial Control
> >> Register.
> >> +  b7 = SCSCR_TIE
> >> +  b6 = SCSCR_RIE
> >> +  b5 = SCSCR_TE
> >> +  b4 = SCSCR_RE
> >> +  b3 = SCSCR_REIE
> >> +  b2 = SCSCR_TOIE
> >> +  b1 = SCSCR_CKE1
> >> +  b0 = SCSCR_CKE0
> > 
> > What is that for exactly ?
> 
> What I can see from 3 different datasheets (sh7372, sh73a0, r8a7740)
> the first 2 bits differ in meaning.
> 
> On r8a7740 it depends: In asynchronous mode the first 2 bits CKE0/1
> define whether you want to use an external clock to drive the baud
> generator or if you want to use the internal SUB clock. If you use the
> SUB clock you can further define if you want to use a subscaled SUB
> clock in the SCSMR register. In synchronous mode you must rely on the
> internal clock for the baud generator and can select if the SCK pin is
> used as clock input or output.

What about adding an optional source clock property to the bindings, that 
would contain the phandle of the source clock ? If the property is absent then 
the internal clock would be used.

How is subscaling used in practice ?

> On sh73a0 and sh7372 it's used to control the output clock SCK (set it
> to high impedance or actually output a clock when in sychronous mode)

Maybe we could add a synchronous mode property to the DT bindings and use it 
to infer the bit values.

> Bit 2 and 3 don't exist in my datasheets.
> 
> The other bits define under which conditions you receive interrupts
> (send FIFO empty, receive FIFO full) and which bits you need to start
> transfers (one bit to start sending, one receiving). The bits 8 to 31
> are used to set up DMA transfers and various interrupt events like
> error status and finish transfers. I haven't included them as they are
> not used in the driver.

If they're not used maybe we can drop them :-)

-- 
Regards,

Laurent Pinchart