Hi Geert,
Thanks for the feedback.
> -----Original Message-----
> From: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Sent: 14 March 2025 14:48
> Subject: Re: [PATCH v4 08/11] can: rcar_canfd: Add shift table to struct rcar_canfd_hw_info
>
> Hi Biju,
>
> Thanks for your patch!
>
> On Thu, 6 Mar 2025 at 13:43, Biju Das <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> > R-Car Gen3 and Gen4 has some differences in the shift bits. Add a
>
> have
>
> > shift table to handle these differences. After this drop the unused
> > functions reg_gen4() and is_gen4().
> >
> > Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
>
> A suggestion for improvement below.
>
> > --- a/drivers/net/can/rcar/rcar_canfd.c
> > +++ b/drivers/net/can/rcar/rcar_canfd.c
> > @@ -90,11 +90,13 @@
> > /* RSCFDnCFDGAFLCFG0 / RSCFDnGAFLCFG0 */ #define
> > RCANFD_GAFLCFG_SETRNC(gpriv, n, x) \
> > (((x) & (gpriv)->info->mask_table[RCANFD_RNC_MASK]) << \
> > - (reg_gen4(gpriv, 16, 24) - ((n) & 1) * reg_gen4(gpriv, 16, 8)))
> > + ((gpriv)->info->shift_table[RCANFD_FIRST_RNC_SH] - ((n) & 1) * \
> > + (gpriv)->info->shift_table[RCANFD_SECOND_RNC_SH]))
>
> Both shifts are dictated by the field width:
> - R-Car Gen4 packs 2 values in a 32-bit word, using a field width
> of 16 bits,
> - R-Car Gen3 packs up to 4 values in a 32-bit word, using a field
> width of 8 bits.
> The odd split in two shifts is due to the MSB-first numbering of the fields. Hence I think it would
> be better to use a field width parameter, and derive the proper shift value from that (like you have
> already done for ICU ;-)
What about ((32 - (n + 1)* field_width) ?
{24,16,8} for n = {0, 1, 2}
And
{16,0} for n = {0, 1}
Cheers,
Biju
