Re: [PATCH v2 08/10] serial: 8250: dw: Add support for DMA flow controlling devices

[Miquel Raynal <miquel.raynal@bootlin.com>]

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>
> > 
> > DW based controllers like the one on Renesas RZ/N1 must be programmed as
> > flow controllers when using DMA.
> > 
> > * 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.
> > 
> > * 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.
> > 
> > Experiments shown that upon Rx timeout, the DMA transaction needed to be
> > manually cleared as well.  
> 
> ...
> 
> > +#define DW_UART_TDMACR	0x10c /* DMA Control Register Transmit Mode */
> > +#define DW_UART_RDMACR	0x110 /* DMA Control Register Receive Mode */  
> 
> These are not Synposys ones.

Ok

> ...
> 
> > +static u32 dw8250_rzn1_get_dmacr_burst(int max_burst)
> > +{
> > +	if (max_burst >= 8)
> > +		return DW_UART_xDMACR_8_WORD_BURST;
> > +	else if (max_burst >= 4)
> > +		return DW_UART_xDMACR_4_WORD_BURST;
> > +	else
> > +		return DW_UART_xDMACR_1_WORD_BURST;
> > +}  
> 
> 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,
Miquèl