[RFC] i2c: i2c-mt65xx and DMA on MT6577 (compatibility issue)

[Boris Lysov <arzamas-16@mail.ee>]

Hello,

I ran into the issue with using i2c-mt65xx driver on MT6577 hardware.
Device tree documentation for the driver says "reg" property requires 2 addresses:
> reg: physical base address of the controller and dma base
Physical base address for MT6577 is 0xC1012000, but AFAIK MT6577 does not have
a DMA base dedicated especially to I2C.

What value has to be used as DMA base on MT6577?

For the sake of example, I did my own research and checked other SoC listed as
compatible in dt-binding doc. I compared the source code of Linux kernels for
devices based on MT6589 and MT6577. See example below.

MT6589, Lenovo A820: https://github.com/jawad6233/Lenovo_A820_Kernel
There are IRQ IDs defined for I2C DMA:
mediatek/platform/mt6589/kernel/core/include/mach/mt_irq.h (line 47)
> #define MT_DMA_I2C1_ID                      (GIC_PRIVATE_SIGNALS + 62)
> #define MT_DMA_I2C2_ID                      (GIC_PRIVATE_SIGNALS + 63)
> #define MT_DMA_I2C3_ID                      (GIC_PRIVATE_SIGNALS + 64)
> #define MT_DMA_I2C4_ID                      (GIC_PRIVATE_SIGNALS + 65)
> #define MT_DMA_I2C5_ID                      (GIC_PRIVATE_SIGNALS + 66)
> #define MT_DMA_I2C6_ID                      (GIC_PRIVATE_SIGNALS + 67)
> #define MT_DMA_I2C7_ID                      (GIC_PRIVATE_SIGNALS + 68)
There are DMA address calculations for various I2C busses:
mediatek/platform/mt6589/kernel/drivers/i2c/i2c.c (line 1135)
> i2c->pdmabase = AP_DMA_BASE + 0x300 + (0x80*(i2c->id));

MT6577, ZTE v970: https://github.com/dragonpt/Kernel_3.4.67_KK_ZTE_v970
There are no IRQ IDs defined for I2C DMA:
mediatek/platform/mt6577/kernel/core/include/mach/mt_irq.h
From line 80 down to line 92 there are DMA addresses for various subsystems except I2C.
And there are no DMA address calculaltions either:
mediatek/platform/mt6577/kernel/drivers/i2c/i2c.c

Please point me to DMA base I should use on MT6577.
Thanks.