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SubjectRE: [PATCH] ARM: OMAP: AM33XX: CAN: d_can: Add support for Bosch D_CAN controller
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On Tue, Apr 03, 2012 at 21:03:40, Marc Kleine-Budde wrote:
> On 04/03/2012 04:29 PM, AnilKumar, Chimata wrote:
> >>>> Please explain why this CAN controller cannot be handled by the existing
> >>>> C_CAN driver, eventually with some extensions. The register layout seems
> >>>> almost identical, at least.
> >>>>
> >>>> Wolfgang.
> >>>>
> >>>
> >>> These are the some of the pointers I can say, why I had gone for separate
> >>> file instead of existing driver:
> >>> * In case of D_CAN driver we can see all the registers are 32bit length
> >>> but in case of C_CAN registers are in 16bit length.
> >>
> >> How many bits in these 32 bit registers are used?
> >
> > In some cases (D_CAN_TXRQ, D_CAN_INTPND, D_CAN_MSGVAL) I have used all the
> > bits, in some cases used few bits.
> >
> > Roughly I can say that its (higher 16bits) % of usages is similar as compare
> > to 16bits
> >
> > While checking the status of TXRequest registers and INT pending register,
> > which is a hot code path, we have to put if checks for register access.
>
> The c_can already has a c_can_read_reg32() function. It's for example
> used in the rx_poll function. You can make it a function pointer (i.e.
> pric->read_reg32()) for easy abstraction.

This won't fit for D_CAN case because offsets are different in c_can compared
to d_can. For example if I read CONTROL_REG register (0x0) in case of d_can,
which will read only control register. In case of c_can it will read
CONTROL_REG + STATUS register values in single read

>
> >>> * Some of the registers, bit masks are different, so we have to add
> >>> checks on every API for differentiating the kind of device
> >>
> >> Which registers are this? Can you give us an example?
> >
> > I am pointing out some of the resisters
> > * Single registers in case of D_CAN but multiple register in case of C_CAN
> > So masks will change MASK, ARB, INTPND
> > * D_CAN_IFCMD is the combination of COMM request and COMM mask registers
>
> Maybe you can use the read_reg32 function on both c_can and d_can.

Above comment applies here as well

>
> regards, Marc
>
> --
> Pengutronix e.K. | Marc Kleine-Budde |
> Industrial Linux Solutions | Phone: +49-231-2826-924 |
> Vertretung West/Dortmund | Fax: +49-5121-206917-5555 |
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>
>



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