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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 |
    > Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
    >
    >



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