[RFC] ns16550: support for UART with broken FIFO

[Jean-Christophe PLAGNIOL-VILLARD]

On 23:40 Tue 17 Jan     , Antony Pavlov wrote:
> On 17 January 2012 18:53, Jean-Christophe PLAGNIOL-VILLARD
> <plagnioj at jcrosoft.com> wrote:
> > On 17:27 Tue 17 Jan     , Antony Pavlov wrote:
> >> On 17 January 2012 17:09, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> >> > On Tue, Jan 17, 2012 at 02:39:06PM +0400, Antony Pavlov wrote:
> >> >> Signed-off-by: Antony Pavlov <antonynpavlov at gmail.com>
> >> >> ---
> >> >>  drivers/serial/serial_ns16550.c |   19 +++++++++++++++++--
> >> >>  include/ns16550.h               |    2 ++
> >> >>  2 files changed, 19 insertions(+), 2 deletions(-)
> >> >>
> >> >> diff --git a/drivers/serial/serial_ns16550.c b/drivers/serial/serial_ns16550.c
> >> >> index 1217a5f..01de964 100644
> >> >> --- a/drivers/serial/serial_ns16550.c
> >> >> +++ b/drivers/serial/serial_ns16550.c
> >> >> @@ -139,6 +139,8 @@ static unsigned int ns16550_calc_divisor(struct console_device *cdev,
> >> >>  static void ns16550_serial_init_port(struct console_device *cdev)
> >> >>  {
> >> >>       unsigned int baud_divisor;
> >> >> +     struct NS16550_plat *plat = (struct NS16550_plat *)
> >> >> +         cdev->dev->platform_data;
> >> >>
> >> >>       /* Setup the serial port with the defaults first */
> >> >>       baud_divisor = ns16550_calc_divisor(cdev, CONFIG_BAUDRATE);
> >> >> @@ -153,7 +155,13 @@ static void ns16550_serial_init_port(struct console_device *cdev)
> >> >>       ns16550_write(cdev, (baud_divisor >> 8) & 0xff, dlm);
> >> >>       ns16550_write(cdev, LCRVAL, lcr);
> >> >>       ns16550_write(cdev, MCRVAL, mcr);
> >> >> -     ns16550_write(cdev, FCRVAL, fcr);
> >> >> +
> >> >> +     if (plat->flags & NS16650_FLAG_DISABLE_FIFO) {
> >> >> +             ns16550_write(cdev, FCRVAL & ~FCR_FIFO_EN, fcr);
> >> >> +     } else {
> >> >> +             ns16550_write(cdev, FCRVAL, fcr);
> >> >> +     }
> >> >
> >> > unnecessary braces here..
> >> >
> >> >> +
> >> >>  #ifdef CONFIG_DRIVER_SERIAL_NS16550_OMAP_EXTENSIONS
> >> >>       ns16550_write(cdev, 0x00,  mdr1);
> >> >>  #endif
> >> >> @@ -211,6 +219,8 @@ static int ns16550_tstc(struct console_device *cdev)
> >> >>  static int ns16550_setbaudrate(struct console_device *cdev, int baud_rate)
> >> >>  {
> >> >>       unsigned int baud_divisor = ns16550_calc_divisor(cdev, baud_rate);
> >> >> +     struct NS16550_plat *plat = (struct NS16550_plat *)
> >> >> +         cdev->dev->platform_data;
> >> >>
> >> >>       ns16550_write(cdev, 0x00, ier);
> >> >>       ns16550_write(cdev, LCR_BKSE, lcr);
> >> >> @@ -218,7 +228,12 @@ static int ns16550_setbaudrate(struct console_device *cdev, int baud_rate)
> >> >>       ns16550_write(cdev, (baud_divisor >> 8) & 0xff, dlm);
> >> >>       ns16550_write(cdev, LCRVAL, lcr);
> >> >>       ns16550_write(cdev, MCRVAL, mcr);
> >> >> -     ns16550_write(cdev, FCRVAL, fcr);
> >> >> +     if (plat->flags & NS16650_FLAG_DISABLE_FIFO) {
> >> >> +             ns16550_write(cdev, FCRVAL & ~FCR_FIFO_EN, fcr);
> >> >> +     } else {
> >> >> +             ns16550_write(cdev, FCRVAL, fcr);
> >> >> +     }
> >> >
> >> > and here. Otherwise this looks ok.
> >>
> >> Ok, I shall remove the braces.
> >>
> >> Sascha!
> >>
> >> We have special OMAP code, e.g.:
> >>
> >> #ifdef CONFIG_DRIVER_SERIAL_NS16550_OMAP_EXTENSIONS
> >>         ns16550_write(cdev, 0x07, mdr1);        /* Disable */
> >> #endif
> >>
> >> I think, that we can change it to something like this:
> >>
> >>     if (plat->flags & NS16650_FLAG_OMAP_EXTENSIONS)
> >>         ns16550_write(cdev, 0x07, mdr1);        /* Disable */
> > I don't like to add dead code in the binary
> > just use
> >        if (IS_ENABLED(CONFIG_...)
> 
> You is right, but there is another point of view.
> 
> If you have defined CONFIG_DRIVER_SERIAL_NS16550_OMAP_EXTENSIONS
> macro, then you will use OMAP extensions for __ALL__ ports, not only
> for OMAP internal port. May be OMAP have no other ports, only internal
> ports with extensions. But in any case it is bad design example: we
> have very special code (OMAP EXTENSIONS) in universal driver
> (ns16550), and this special code works without checking presents of
> the extensions.
> 
> I don't like dead code too. So there are another solutions:
> 
> #ifdef CONFIG_DRIVER_SERIAL_NS16550_OMAP_EXTENSIONS
>         if (plat->flags & NS16650_FLAG_OMAP_EXTENSIONS)
>             ns16550_write(cdev, 0x07, mdr1);        /* Disable */
> #endif
> 
> or even
>         if (IS_ENABLED(CONFIG_DRIVER_SERIAL_NS16550_OMAP_EXTENSIONS) &&
>          plat->flags & NS16650_FLAG_OMAP_EXTENSIONS)
>             ns16550_write(cdev, 0x07, mdr1);        /* Disable */
this one

Best Regards,
J.
> -- 
> Best regards,
>   Antony Pavlov