Re: [PATCH 06/12] macfb: implement mode sense to allow display type to be detected

[BALATON Zoltan]

On Mon, 4 Oct 2021, Laurent Vivier wrote:
> Le 02/10/2021 à 13:00, Mark Cave-Ayland a écrit :
> > The MacOS toolbox ROM uses the monitor sense to detect the display type and then
> > offer a fixed set of resolutions and colour depths accordingly. Implement the
> > monitor sense using information found in Apple Technical Note HW26: "Macintosh
> > Quadra Built-In Video" along with some local experiments.
> >
> > Since the default configuration is 640 x 480 with 8-bit colour then hardcode
> > the sense register to return MACFB_DISPLAY_VGA for now.
> >
> > Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> > ---
> >  hw/display/macfb.c         | 117 ++++++++++++++++++++++++++++++++++++-
> >  hw/display/trace-events    |   2 +
> >  include/hw/display/macfb.h |  20 +++++++
> >  3 files changed, 137 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/display/macfb.c b/hw/display/macfb.c
> > index 62c2727a5b..5c95aa4a11 100644
> > --- a/hw/display/macfb.c
> > +++ b/hw/display/macfb.c
> > @@ -28,8 +28,66 @@
> >  #define MACFB_PAGE_SIZE 4096
> >  #define MACFB_VRAM_SIZE (4 * MiB)
> >
> > -#define DAFB_RESET      0x200
> > -#define DAFB_LUT        0x213
> > +#define DAFB_MODE_SENSE     0x1c
> > +#define DAFB_RESET          0x200
> > +#define DAFB_LUT            0x213
> > +
> > +
> > +/*
> > + * Quadra sense codes taken from Apple Technical Note HW26:
> > + * "Macintosh Quadra Built-In Video". The sense codes and
>
> https://developer.apple.com/library/archive/technotes/hw/hw_26.html

URLs may change or go away so I think it's better to reference by title in 
comments, then one can find it by that whereas a stale URL is not much 
help a few years from now.

Regards,
BALATON Zoltan

> > + * extended sense codes have different meanings:
> > + *
> > + * Sense:
> > + *    bit 2: SENSE2 (pin 10)
> > + *    bit 1: SENSE1 (pin 7)
> > + *    bit 0: SENSE0 (pin 4)
> > + *
> > + * 0 = pin tied to ground
> > + * 1 = pin unconnected
> > + *
> > + * Extended Sense:
> > + *    bit 2: pins 4-10
> > + *    bit 1: pins 10-7
> > + *    bit 0: pins 7-4
> > + *
> > + * 0 = pins tied together
> > + * 1 = pins unconnected
> > + *
> > + * Reads from the sense register appear to be active low, i.e. a 1 indicates
> > + * that the pin is tied to ground, a 0 indicates the pin is disconnected.
> > + *
> > + * Writes to the sense register appear to activate pulldowns i.e. a 1 enables
> > + * a pulldown on a particular pin.
> > + *
> > + * The MacOS toolbox appears to use a series of reads and writes to first
> > + * determine if extended sense is to be used, and then check which pins are
> > + * tied together in order to determine the display type.
> > + */
> > +
> > +typedef struct MacFbSense {
> > +    uint8_t type;
> > +    uint8_t sense;
> > +    uint8_t ext_sense;
> > +} MacFbSense;
> > +
> > +static MacFbSense macfb_sense_table[] = {
> > +    { MACFB_DISPLAY_APPLE_21_COLOR, 0x0, 0 },
> > +    { MACFB_DISPLAY_APPLE_PORTRAIT, 0x1, 0 },
> > +    { MACFB_DISPLAY_APPLE_12_RGB, 0x2, 0 },
> > +    { MACFB_DISPLAY_APPLE_2PAGE_MONO, 0x3, 0 },
> > +    { MACFB_DISPLAY_NTSC_UNDERSCAN, 0x4, 0 },
> > +    { MACFB_DISPLAY_NTSC_OVERSCAN, 0x4, 0 },
> > +    { MACFB_DISPLAY_APPLE_12_MONO, 0x6, 0 },
> > +    { MACFB_DISPLAY_APPLE_13_RGB, 0x6, 0 },
> > +    { MACFB_DISPLAY_16_COLOR, 0x7, 0x3 },
> > +    { MACFB_DISPLAY_PAL1_UNDERSCAN, 0x7, 0x0 },
> > +    { MACFB_DISPLAY_PAL1_OVERSCAN, 0x7, 0x0 },
> > +    { MACFB_DISPLAY_PAL2_UNDERSCAN, 0x7, 0x6 },
> > +    { MACFB_DISPLAY_PAL2_OVERSCAN, 0x7, 0x6 },
> > +    { MACFB_DISPLAY_VGA, 0x7, 0x5 },
> > +    { MACFB_DISPLAY_SVGA, 0x7, 0x5 },
>
> Perhaps it could be interesting to also have the "no external monitor" entry?
> But generally not to have monitor prevents the boot of MacOS.
>
> ...
>
> Reviewed-by: Laurent Vivier <laurent@vivier.eu>