ESP32 BluePill with GMG12864 display - questions

[navado]

Hello
I'm trying to bring up ESP32 with GMG12864 that I have in the spares and encountering several questions using u8g2.

My setup:

Display: GMG12864-06D

#define CS_PIN PC14
#define RST_PIN PC15
#define RS_PIN PA0
#define SCL_PIN PA5
#define SDO_PIN PA6
#define SDI_PIN PA7
#define BACKLIGHT_PIN PinName::PA_1
#define LED_BRD PC13

#define CONTRAST_SETTING 0x3A

U8G2_ST7565_EA_DOGM128_1_4W_SW_SPI lcd(U8G2_R2,
                                       /* clock=*/SCL_PIN,
                                       /* data=*/SDO_PIN,
                                       /* cs=*/CS_PIN,
                                       /* dc=*/RS_PIN,
                                       /* reset=*/RST_PIN
                                       );

Now the questions

1. How to initialize the display with HW SPI?

I dug into different implementations of constructors initializing ST7565 with HW SPI and it looks like they're all referring to hard coded pin numbers that are not corresponding to BluePill pins. Probably I'm missing something, but also I'm unable to find a working config with HW SPI

2. What's the dc pin in the constructor?

I just tried the RS pin from the display and it worked, but why?

3. How to configure offset for the display?

I'm getting 125x64 useful pixels shifted 4 pixels right if initializing with U8G2_R2 and shift of 8 pixels if initialized with U8G2_R0 giving it 121x64 useful pixels.

Appreciate clues to the right direction.