[PATCH 4/4] lib: utils/serial: Ensure baudrate is non-zero before using
Andrew Jones
ajones at ventanamicro.com
Wed Jul 20 22:35:57 PDT 2022
On Thu, Jul 21, 2022 at 01:25:44AM +0800, Xiang W wrote:
> 在 2022-07-20星期三的 19:16 +0200，Andrew Jones写道：
> > On Wed, Jul 20, 2022 at 11:12:18PM +0800, Xiang W wrote:
> > > 在 2022-07-18星期一的 19:20 +0200，Andrew Jones写道：
> > > > RISC-V doesn't generate exceptions on divide-by-zero, but the result,
> > > > all bits set, is not likely what people expect either. In all cases
> > > > where we divide by baudrate there's a chance it's zero (when the DT
> > > > it came from is "bad"). To avoid difficult to debug situations, leave
> > > > baudrate dependent registers alone when baudrate is zero, as, also in
> > > > all cases, it appears we can skip initialization of those registers
> > > > and still [hopefully] have a functioning UART.
> > > >
> > > > Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
> > > If the parameter is wrong we should skip initialization and should not
> > > execute sbi_console_set_device.
> >
> > Hi Xiang,
> >
> > While there should be some DT validation somewhere that points out bad
> > parameters, I don't think opensbi is the best place to do it, especially
> > for UART configuration. While we certainly can't progress in all cases
> > we detect bad input, in the case of a zero baudrate I believe we can, as
> > it appears setting baudrate registers is typically optional for UARTs.
> >
> > We could also consider adding a log buffer which early init can write
> > errors and warnings to. After the console has been initialized (with
> > our best effort) we can then output all the errors and warnings from the
> > log buffer. If we had something like that, then we could add a warning
> > about the baudrate to that log along with warnings/errors for any other
> > DT parameters we fail to validate but attempt to work around.
> >
> > Thanks,
> > drew
> I mean:
>
> int xxx_uart_init(...)
> {
> if (baudrate == 0)
> return 0;
> ...
> // console_dev should not be set because initialization failed
> }
I understood your suggestion, but I disagree. If it's possible to
initialize a device without all information in the DT being present or
valid, then, IMHO, opensbi should do so. Outputting errors/warnings
is good, but giving up turns opensbi into a DT validator which it isn't
well equipped to be. It's a particularly bad DT validator when parsing
UART DT nodes or any other nodes before the console is available.
I do agree that if we try to initialize the console despite detecting
bad information in the DT that we risk not having a working console
and not easily understanding why. I think the early log buffer I
suggest above could help with that. When debugging the first thing one
would do is to dump the contents of that buffer to see if any messages
can point them in the right direction.
I'll try to pull together some log buffer patches and post for
discussion.
Thanks,
drew
>
> >
> > >
> > > Regards,
> > > Xiang W
> > > > ---
> > > > lib/utils/serial/gaisler-uart.c | 2 +-
> > > > lib/utils/serial/shakti-uart.c | 8 ++++++--
> > > > lib/utils/serial/sifive-uart.c | 2 +-
> > > > lib/utils/serial/uart8250.c | 7 +++++--
> > > > 4 files changed, 13 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/lib/utils/serial/gaisler-uart.c b/lib/utils/serial/gaisler-uart.c
> > > > index 5f30ee43b719..eec75cca0c98 100644
> > > > --- a/lib/utils/serial/gaisler-uart.c
> > > > +++ b/lib/utils/serial/gaisler-uart.c
> > > > @@ -70,7 +70,7 @@ int gaisler_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
> > > > uart_base = (volatile char *)base;
> > > >
> > > > /* Configure baudrate */
> > > > - if (in_freq)
> > > > + if (in_freq && baudrate)
> > > > set_reg(UART_REG_SCALER, in_freq / (baudrate * 8 + 7));
> > > >
> > > > ctrl = get_reg(UART_REG_CTRL);
> > > > diff --git a/lib/utils/serial/shakti-uart.c b/lib/utils/serial/shakti-uart.c
> > > > index 5f2fe75c9f33..2f09f141b9cf 100644
> > > > --- a/lib/utils/serial/shakti-uart.c
> > > > +++ b/lib/utils/serial/shakti-uart.c
> > > > @@ -47,8 +47,12 @@ static struct sbi_console_device shakti_console = {
> > > > int shakti_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
> > > > {
> > > > uart_base = (volatile char *)base;
> > > > - u16 baud = (u16)(in_freq/(16 * baudrate));
> > > > - writew(baud, uart_base + REG_BAUD);
> > > > + u16 baud;
> > > > +
> > > > + if (baudrate) {
> > > > + baud = (u16)(in_freq / (16 * baudrate));
> > > > + writew(baud, uart_base + REG_BAUD);
> > > > + }
> > > >
> > > > sbi_console_set_device(&shakti_console);
> > > >
> > > > diff --git a/lib/utils/serial/sifive-uart.c b/lib/utils/serial/sifive-uart.c
> > > > index 7078611a5274..3581d47a6d4b 100644
> > > > --- a/lib/utils/serial/sifive-uart.c
> > > > +++ b/lib/utils/serial/sifive-uart.c
> > > > @@ -97,7 +97,7 @@ int sifive_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
> > > > uart_baudrate = baudrate;
> > > >
> > > > /* Configure baudrate */
> > > > - if (in_freq)
> > > > + if (in_freq && baudrate)
> > > > set_reg(UART_REG_DIV, uart_min_clk_divisor(in_freq, baudrate));
> > > >
> > > > /* Disable interrupts */
> > > > diff --git a/lib/utils/serial/uart8250.c b/lib/utils/serial/uart8250.c
> > > > index 38ea11af4d31..99bf1bf733f2 100644
> > > > --- a/lib/utils/serial/uart8250.c
> > > > +++ b/lib/utils/serial/uart8250.c
> > > > @@ -93,7 +93,7 @@ static struct sbi_console_device uart8250_console = {
> > > > int uart8250_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,
> > > > u32 reg_width, u32 reg_offset)
> > > > {
> > > > - u16 bdiv;
> > > > + u16 bdiv = 0;
> > > >
> > > > uart8250_base = (volatile char *)base + reg_offset;
> > > > uart8250_reg_shift = reg_shift;
> > > > @@ -101,7 +101,10 @@ int uart8250_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,
> > > > uart8250_in_freq = in_freq;
> > > > uart8250_baudrate = baudrate;
> > > >
> > > > - bdiv = (uart8250_in_freq + 8 * uart8250_baudrate) / (16 * uart8250_baudrate);
> > > > + if (uart8250_baudrate) {
> > > > + bdiv = (uart8250_in_freq + 8 * uart8250_baudrate) /
> > > > + (16 * uart8250_baudrate);
> > > > + }
> > > >
> > > > /* Disable all interrupts */
> > > > set_reg(UART_IER_OFFSET, 0x00);
> > > > --
> > > > 2.36.1
> > > >
> > > >
> > >
> > >
> > >
> > > --
> > > opensbi mailing list
> > > opensbi at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/opensbi
>
>
More information about the opensbi
mailing list