Hi Miquel, CC esmil On Fri, Mar 11, 2022 at 10:39 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Miquel, > > On Thu, Mar 10, 2022 at 5:17 PM Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote: > > From: Phil Edworthy <phil.edworthy@xxxxxxxxxxx> > > > > The Renesas RZ/N1 devices have a modified Synopsys DW UART. The > > modifications are mostly related to the DMA handlnig, and so this patch > > adds support for DMA. > > > > The RZ/N1 UART must be used with the peripheral as the flow > > controller. This means the DMA length should also be programmed into > > UART registers. > > > > Aside from this, there are some points to note about DMA burst sizes. > > First, DMA must not remove all of the data from the rx FIFO. Otherwise, > > we do not get a 'character timeout' interrupt, and so do not know that > > we should push data up the serial stack. Therefore, we have the rx > > threshold for generating an interrupt set to half the FIFO depth (this > > is the default for 16550A), and set the DMA burst size when reading the > > FIFO to a quarter of the FIFO depth. > > > > Second, when transmitting data using DMA, the burst size must be limited > > to 1 byte to handle then case when transmitting just 1 byte. Otherwise > > the DMA doesn't complete the burst, and nothing happens. > > > > Signed-off-by: Phil Edworthy <phil.edworthy@xxxxxxxxxxx> > > Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx> > > Thanks for your patch! > > > --- a/drivers/tty/serial/8250/8250_dma.c > > +++ b/drivers/tty/serial/8250/8250_dma.c > > > @@ -501,6 +589,8 @@ static int dw8250_probe(struct platform_device *pdev) > > data->msr_mask_off |= UART_MSR_TERI; > > } > > > > + data->is_rzn1 = of_device_is_compatible(dev->of_node, "renesas,rzn1-uart"); > > Explicit checks for compatible values are frowned upon if you have > a match table. > Please handle this through of_device.data, cfr. the various quirks. Oops, these are not yet upstream, but present in my tree due to including support for StarLight, cfr. https://github.com/esmil/linux/commits/visionfive/drivers/tty/serial/8250/8250_dw.c But you do already have: + { .compatible = "renesas,rzn1-uart", .data = &rzn1_pdata }, since "[PATCH 4/7] serial: 8250_dw: Provide the RZN1 CPR register value". > Please rename "is_rzn1" to something that describes the feature. > > > + > > /* Always ask for fixed clock rate from a property. */ > > device_property_read_u32(dev, "clock-frequency", &p->uartclk); Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
