RE: [PATCH v4 5/6] serial: 8250_em: Use pseudo offset for UART_FCR

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Fri, 17 Feb 2023, Biju Das wrote:

> Hi Ilpo,
> 
> Thanks for the feedback.
> 
> > Subject: Re: [PATCH v4 5/6] serial: 8250_em: Use pseudo offset for UART_FCR
> > 
> > On Fri, 17 Feb 2023, Biju Das wrote:
> > 
> > > UART_FCR shares the same offset with UART_IIR. We cannot use UART_FCR
> > > in serial8250_em_serial_in() as it overlaps with UART_IIR.
> > >
> > > This patch introduces a macro UART_FCR_EM with a high value to avoid
> > > overlapping with existing UART_* register defines.
> > >
> > > This will help us to use UART_FCR_EM consistently in serial8250_em_
> > > serial{_in/_out} function to read/write FCR register.
> > >
> > > Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> > > ---
> > > v4:
> > >  * New patch. Used UART_FCR_EM for read/write of FCR register.
> > > ---
> > >  drivers/tty/serial/8250/8250_em.c | 13 ++++++++++++-
> > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/tty/serial/8250/8250_em.c
> > > b/drivers/tty/serial/8250/8250_em.c
> > > index 499d7a8847ec..4165fd3bb17a 100644
> > > --- a/drivers/tty/serial/8250/8250_em.c
> > > +++ b/drivers/tty/serial/8250/8250_em.c
> > > @@ -19,6 +19,13 @@
> > >  #define UART_DLL_EM 9
> > >  #define UART_DLM_EM 10
> > >
> > > +/*
> > > + * A high value for UART_FCR_EM avoids overlapping with existing
> > > +UART_*
> > > + * register defines. UART_FCR_EM_HW is the real HW register offset.
> > > + */
> > > +#define UART_FCR_EM 0x10003
> > > +#define UART_FCR_EM_HW 3
> > > +
> > >  struct serial8250_em_priv {
> > >  	int line;
> > >  };
> > > @@ -29,12 +36,14 @@ static void serial8250_em_serial_out(struct uart_port
> > *p, int offset, int value)
> > >  	case UART_TX: /* TX @ 0x00 */
> > >  		writeb(value, p->membase);
> > >  		break;
> > > -	case UART_FCR: /* FCR @ 0x0c (+1) */
> > 
> > 8250_port wants this to remain in place, I think. Otherwise it's attempts to
> > set UART_FCR will end up into wrong destination.
> 
> Oops, next patch has this change.
> 
> +	case UART_FCR:
> +		serial8250_em_reg_update(p, UART_FCR_EM, value);
> 
> I just need to keep UART_FCR for this patch and 
> remove it from "serial8250_em_serial_out_helper" on the next patch

IMHO, the extra layer + _helper seems pretty unnecessary. I don't see any 
useful thing it achieves over just having to serial_out functions.

-- 
 i.