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

[Bin Meng]

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.

> +       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,
Bin