Add new property/value mailbox channel

[popcornmix]

Suggestion for property/value message passing interface from ARM to GPU.

We have a generic message passing structure. The first word is always the property of interest (could be small integers or fourcc codes).
The remainder of the structure is property specific data whose length depends on the property. This data is used for both input and output data.

define MBOX_CHAN_GETPROP 8

define MBOX_CHAN_SETPROP 9

// generic property structure
struct property_s {
uint32_t property;
uint32_t data[];
}

// get property
void *property = <>
uint32_t success;
mbox_write(MBOX_CHAN_GETPROP, property);
mbox_read(MBOX_CHAN_GETPROP, &success);

// set property
void *property = <>
uint32_t success;
mbox_write(MBOX_CHAN_SETPROP, property);
mbox_read(MBOX_CHAN_SETPROP, &success);

Example:

define CLOCK_EMMC 1

struct property_one_word_s {
uint32_t property;
uint32_t value;
} *emmc_clock;

uint32_t success;
emmc_clock =
emmc_clock->property = CLOCK_EMMC;
emmc_clock->value = 50000000;
_wmb();
mbox_write(MBOX_CHAN_SETPROP, emmc_clock);
mbox_read(MBOX_CHAN_SETPROP, &success);
_rmb();

We could also use this to handle the existing framebuffer allocation and power control in a more consistent way.

Any config.txt properties can be retrieved with this mechanism. E.g.
struct property_one_word_one_string_s {
uint32_t property;
uint32_t value;
uint8_t string[MAX_STRING];
} *config_txt;

Similarly cmdline.txt and other ATAGs (e.g. memory size) can be got.

Properties that can be got or set:
CLOCK_EMMC
CLOCK_UART
CLOCK_ARM
CLOCK_CORE
CLOCK_V3D
CLOCK_H264
CLOCK_ISP
POWER_CONTROL
FRAMEBUFFER

Properties that can be got:
CMDLINE
CONFIG_STRING
SERIAL_NUM
BOARD_REV
MAC_ADDRESS
DISPLAY_WIDTH
DISPLAY_HEIGHT
DISPLAY_DEPTH
DMA_CHANS
MEMORY_SIZE

Any additional suggestions?

[popcornmix]

Moved to: raspberrypi/firmware#47