[PATCH] serial: ns16550: Handle zero <clock-frequency> value

[Bin Meng]

Hi Simon,

On Thu, Feb 4, 2021 at 5:42 AM Simon Glass <sjg at chromium.org> wrote:
>
> Hi Bin,
>
> On Wed, 3 Feb 2021 at 07:42, Bin Meng <bmeng.cn at gmail.com> wrote:
> >
> > A working device tree node of ns16550 should never be populated
> > with value zero for the <clock-frequency> property. Unfortunately
> > this is the case for the QEMU ppce500 target.
> >
> > Let's try to assign plat->clock to CONFIG_SYS_NS16550_CLK as the
> > last resort to handle such case.
> >
> > This commit should be reverted when:
> >
> > - The following QEMU patch [1] is merged, and
> > - U-Boot CI has upgraded its QEMU version that contains the fix
> >
> > [1] http://patchwork.ozlabs.org/project/qemu-devel/patch/1612362288-22216-2-git-send-email-bmeng.cn@gmail.com/
> >
> > Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> > ---
> >
> >  drivers/serial/ns16550.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
> > index da903c1..a1593a2 100644
> > --- a/drivers/serial/ns16550.c
> > +++ b/drivers/serial/ns16550.c
> > @@ -563,6 +563,8 @@ int ns16550_serial_of_to_plat(struct udevice *dev)
> >         if (!plat->clock)
> >                 plat->clock = dev_read_u32_default(dev, "clock-frequency",
> >                                                    CONFIG_SYS_NS16550_CLK);
> > +       if (!plat->clock)
> > +               plat->clock = CONFIG_SYS_NS16550_CLK;
>
> This is already done in the line above...does that not work?

The line above only works if there is no <clock-frequency> in the
device tree. Since the device tree does provide a <clock-frequency>,
the default one was never used.

>
> >         if (!plat->clock) {
> >                 debug("ns16550 clock not defined\n");
> >                 return -EINVAL;

Regards,
Bin