[PATCH 2/4] serial: s5p: Use livetree API to get "id" property

[Sam Protsenko]

Hi Simon,

On Tue, Nov 7, 2023 at 10:26 PM Simon Glass <sjg at chromium.org> wrote:
>
> Hi Sam,
>
> On Tue, 7 Nov 2023 at 12:06, Sam Protsenko <semen.protsenko at linaro.org> wrote:
> >
> > Use dev_read_u8_default() instead of fdtdec_get_int() to read the "id"
> > property from device tree, as suggested in [1]. dev_* API is already
> > used in this driver, so there is no reason to stick to fdtdec_* API.
> > This also fixes checkpatch warning:
> >
> >     WARNING: Use the livetree API (dev_read_...)
> >
> > [1] doc/develop/driver-model/livetree.rst
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
> > ---
> >  drivers/serial/serial_s5p.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/drivers/serial/serial_s5p.c b/drivers/serial/serial_s5p.c
> > index 177215535676..c57bdd059ea6 100644
> > --- a/drivers/serial/serial_s5p.c
> > +++ b/drivers/serial/serial_s5p.c
> > @@ -20,8 +20,6 @@
> >  #include <serial.h>
> >  #include <clk.h>
> >
> > -DECLARE_GLOBAL_DATA_PTR;
> > -
> >  enum {
> >         PORT_S5P = 0,
> >         PORT_S5L
> > @@ -220,8 +218,7 @@ static int s5p_serial_of_to_plat(struct udevice *dev)
> >
> >         plat->reg = (struct s5p_uart *)addr;
> >         plat->reg_width = dev_read_u32_default(dev, "reg-io-width", 1);
> > -       plat->port_id = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev),
> > -                                       "id", dev_seq(dev));
> > +       plat->port_id = dev_read_u8_default(dev, "id", dev_seq(dev));
> >
> >         if (port_type == PORT_S5L) {
> >                 plat->rx_fifo_count_shift = S5L_RX_FIFO_COUNT_SHIFT;
> > --
> > 2.39.2
> >
>
> Really this property should not be needed anymore. Can you figure out
> how to drop it?
>

The 'port_id' seems to be needed for ARCH_EXYNOS4 boards. Because
Exynos4 doesn't have proper DM clocks, it uses 'id' property to get
corresponding UART clock frequency from its mach code.

Here is what's happening in the serial driver in case of Exynos4:

  1. get_uart_clk(port_id) is called
  2. which in turn calls exynos4_get_uart_clk(port_id)
  3. which uses "port_id" value to read corresponding bits of of
CLK_SRC_PERIL0 register
  4. those bits are used to get corresponding PLL clock's frequency
  5. which is in turn used to calculate UART clock rate
  6. calculated rate is returned by get_uart_clk() to serial driver

So I don't see any *easy* way we can get rid of that id property.

The proper way of doing that would require converting Exynos4 clock
code to CCF (enabling CONFIG_CLK_EXYNOS). Which of course also means
implementing clocks in dts, akin to kernel's exynos4.dtsi. Then it'll
be possible to get rid of 'id' property.

Maybe I'm missing something, please let me know.

Thanks!

> Regards,
> Simon