[PATCH] serial: a3720: Implement pending method for output direction

[Pali Rohár]

On Friday 15 January 2021 15:50:46 Stefan Roese wrote:
> On 14.01.21 15:46, Pali Rohár wrote:
> > To check if some output characters are waiting either in Transmitter
> > Holding Register or Transmitter Shift Register we need to look at
> > TX_EMPTY bit of UART Status Register.
> > 
> > Signed-off-by: Pali Rohár <pali at kernel.org>
> 
> Reviewed-by: Stefan Roese <sr at denx.de>
> 
> BTW: How did you detect this issue?

During debugging both TF-A and linux kernel as they were eating
characters sent via A3720 UART. Details are in kernel and TF-A patches:

https://lore.kernel.org/linux-serial/20201223191931.18343-1-pali@kernel.org/
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/7734

I have not spotted this issue in U-Boot (only in TF-A and kernel), but I
decided to look also at the U-Boot A3720 UART implementation... And find
out that it is incomplete too, ignoring 'bool input' function argument.

> Thanks,
> Stefan
> 
> > ---
> >   drivers/serial/serial_mvebu_a3700.c | 10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/serial/serial_mvebu_a3700.c b/drivers/serial/serial_mvebu_a3700.c
> > index fb43f88eaf..909901c9f0 100644
> > --- a/drivers/serial/serial_mvebu_a3700.c
> > +++ b/drivers/serial/serial_mvebu_a3700.c
> > @@ -23,6 +23,7 @@ struct mvebu_platdata {
> >   #define UART_POSSR_REG		0x14
> >   #define UART_STATUS_RX_RDY	0x10
> > +#define UART_STATUS_TX_EMPTY	0x40
> >   #define UART_STATUS_TXFIFO_FULL	0x800
> >   #define UART_CTRL_RXFIFO_RESET	0x4000
> > @@ -59,8 +60,13 @@ static int mvebu_serial_pending(struct udevice *dev, bool input)
> >   	struct mvebu_platdata *plat = dev_get_platdata(dev);
> >   	void __iomem *base = plat->base;
> > -	if (readl(base + UART_STATUS_REG) & UART_STATUS_RX_RDY)
> > -		return 1;
> > +	if (input) {
> > +		if (readl(base + UART_STATUS_REG) & UART_STATUS_RX_RDY)
> > +			return 1;
> > +	} else {
> > +		if (!(readl(base + UART_STATUS_REG) & UART_STATUS_TX_EMPTY))
> > +			return 1;
> > +	}
> >   	return 0;
> >   }
> > 
> 
> 
> Viele Grüße,
> Stefan
> 
> -- 
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