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Date:   Tue, 29 Mar 2022 10:29:51 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     linux-renesas-soc@vger.kernel.org,
        Magnus Damm <magnus.damm@gmail.com>,
        Gareth Williams <gareth.williams.jx@renesas.com>,
        Phil Edworthy <phil.edworthy@renesas.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Milan Stevanovic <milan.stevanovic@se.com>,
        Jimmy Lalande <jimmy.lalande@se.com>,
        Pascal Eberhard <pascal.eberhard@se.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Herve Codina <herve.codina@bootlin.com>,
        Clement Leger <clement.leger@bootlin.com>,
        linux-serial@vger.kernel.org
Subject: Re: [PATCH v2 08/10] serial: 8250: dw: Add support for DMA flow
 controlling devices
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        <20220317174627.360815-9-miquel.raynal@bootlin.com>
        <YjSWM5ilahNBXF1b@smile.fi.intel.com>
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Hi Andy,

andriy.shevchenko@linux.intel.com wrote on Fri, 18 Mar 2022 16:24:51
+0200:

> On Thu, Mar 17, 2022 at 06:46:25PM +0100, Miquel Raynal wrote:
> > From: Phil Edworthy <phil.edworthy@renesas.com>
> >=20
> > DW based controllers like the one on Renesas RZ/N1 must be programmed as
> > flow controllers when using DMA.
> >=20
> > * Table 11.45 of the system manual, "Flow Control Combinations", states
> >   that using UART with DMA requires setting the DMA in the peripheral
> >   flow controller mode regardless of the direction.
> >=20
> > * Chapter 11.6.1.3 of the system manual, "Basic Interface Definitions",
> >   explains that the burst size in the above case must be configured in
> >   the peripheral's register DEST/SRC_BURST_SIZE.
> >=20
> > Experiments shown that upon Rx timeout, the DMA transaction needed to be
> > manually cleared as well. =20
>=20
> ...
>=20
> > +#define DW_UART_TDMACR	0x10c /* DMA Control Register Transmit Mode */
> > +#define DW_UART_RDMACR	0x110 /* DMA Control Register Receive Mode */ =
=20
>=20
> These are not Synposys ones.

Ok

> ...
>=20
> > +static u32 dw8250_rzn1_get_dmacr_burst(int max_burst)
> > +{
> > +	if (max_burst >=3D 8)
> > +		return DW_UART_xDMACR_8_WORD_BURST;
> > +	else if (max_burst >=3D 4)
> > +		return DW_UART_xDMACR_4_WORD_BURST;
> > +	else
> > +		return DW_UART_xDMACR_1_WORD_BURST;
> > +} =20
>=20
> Redundant 'else' in all cases.

I'm sorry but dropping the else statement here does not make any
sense. I find it much easier to the eyes the current way.

Thanks,
Miqu=C3=A8l