[PATCH v4 2/2] x86: Update cbmem driver

[Simon Glass]

Hi Bin,

On Tue, 19 Sept 2023 at 02:47, Bin Meng <bmeng.cn at gmail.com> wrote:
>
> Hi Simon,
>
> On Mon, Sep 11, 2023 at 3:13 AM Simon Glass <sjg at chromium.org> wrote:
> >
> > This driver is not actually built since a Kconfig was never created for
> > it.
> >
> > Add a Kconfig (which is already implied by COREBOOT) and update the
> > implementation to avoid using unnecessary memory. Drop the #ifdef at the
> > top since we can rely on Kconfig to get that right.
> >
> > To enable it (in addition to serial and video), use:
> >
> >    setenv stdout serial,vidconsole,cbmem
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> > Changes in v4:
> > - Add some comments to help understand the overflow mechanism
> >
> > Changes in v2:
> > - Update to support the new overflow mechanism
> >
> >  drivers/misc/Kconfig         |  8 +++++++
> >  drivers/misc/cbmem_console.c | 43 ++++++++++++++++++++++--------------
> >  2 files changed, 34 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > index a6e3f62ecb09..c930e4a361bf 100644
> > --- a/drivers/misc/Kconfig
> > +++ b/drivers/misc/Kconfig
> > @@ -122,6 +122,14 @@ config VEXPRESS_CONFIG
> >           configuration bus on the Arm Versatile Express boards via
> >           a sysreg driver.
> >
> > +config CBMEM_CONSOLE
> > +       bool "Write console output to coreboot cbmem"
> > +       depends on X86
> > +       help
> > +         Enables console output to the cbmem console, which is a memory
> > +         region set up by coreboot to hold a record of all console output.
> > +         Enable this only if booting from coreboot.
> > +
> >  config CMD_CROS_EC
> >         bool "Enable crosec command"
> >         depends on CROS_EC
> > diff --git a/drivers/misc/cbmem_console.c b/drivers/misc/cbmem_console.c
> > index 8bbe33d414da..3cbe9fb1a46a 100644
> > --- a/drivers/misc/cbmem_console.c
> > +++ b/drivers/misc/cbmem_console.c
> > @@ -5,27 +5,37 @@
> >
> >  #include <common.h>
> >  #include <console.h>
> > -#ifndef CONFIG_SYS_COREBOOT
> > -#error This driver requires coreboot
> > -#endif
> > -
> >  #include <asm/cb_sysinfo.h>
> >
> > -struct cbmem_console {
> > -       u32 buffer_size;
> > -       u32 buffer_cursor;
> > -       u8  buffer_body[0];
> > -}  __attribute__ ((__packed__));
> > -
> > -static struct cbmem_console *cbmem_console_p;
> > -
> >  void cbmemc_putc(struct stdio_dev *dev, char data)
> >  {
> > -       int cursor;
> > +       const struct sysinfo_t *sysinfo = cb_get_sysinfo();
> > +       struct cbmem_console *cons;
> > +       uint pos, flags;
> > +
> > +       if (!sysinfo)
> > +               return;
> > +       cons = sysinfo->cbmem_cons;
> > +       if (!cons)
> > +               return;
> > +
> > +       pos = cons->cursor & CBMC_CURSOR_MASK;
> > +
> > +       /* preserve the overflow flag if present */
> > +       flags = cons->cursor & ~CBMC_CURSOR_MASK;
> > +
> > +       cons->body[pos++] = data;
> > +
> > +       /*
> > +        * Deal with overflow - the flag may be cleared by another program which
> > +        * reads the buffer out, e.g. Linux
> > +        */
>
> U-Boot is not memory resident, so this does not sound like a correct
> overflow mechanism to me.

I am not sure what you mean. This logic is used in coreboot and some
payloads, so I want to do the same in U-Boot. It basically let's
U-Boot handle an overflow properly by setting the overflow flag. A
later program (e.g. Linux) can then tell that that an overflow
occurred.


>
> > +       if (pos >= cons->size) {
> > +               pos = 0;
> > +               flags |= CBMC_OVERFLOW;
> > +       }
> >
> > -       cursor = cbmem_console_p->buffer_cursor++;
> > -       if (cursor < cbmem_console_p->buffer_size)
> > -               cbmem_console_p->buffer_body[cursor] = data;
> > +       cons->cursor = flags | pos;
> >  }
> >
> >  void cbmemc_puts(struct stdio_dev *dev, const char *str)
> > @@ -40,7 +50,6 @@ int cbmemc_init(void)
> >  {
> >         int rc;
> >         struct stdio_dev cons_dev;
> > -       cbmem_console_p = lib_sysinfo.cbmem_cons;
> >
> >         memset(&cons_dev, 0, sizeof(cons_dev));
> >
>

Regards,
Simon