[RFC PATCH v3 2/2] clk: exynos5420: Make sure MDMA0 clock is enabled during suspend

[Javier Martinez Canillas]

On 04/07/2015 12:59 PM, Javier Martinez Canillas wrote:
> 
> So IIUC the CG_STATUS0 bits were a red herring and the real problem
> is that the aclk266_g2d needs to be enabled during suspend (although
> we still don't know why).
> 
> It seems were are at a dead end now. Without being able to ask the HW
> Samsung folks we would never know what's going on here...
> 

Ok, I found another interesting data point. ACLK_266_G2D has as
constraints that CG_STATUS0[21:22] needs to be 0 before gating
the clock and as I mentioned before those are associated with
the SSS and SSS_SLIM HW crypto modules according the docs I've.

So I looked at the clock used by the SSS module and found that
CLK_SSS parent is ACLK_266_G2D but CLK_SSS is never requested
since drivers/crypto/s5p-sss.c isn't built for exynos_defconfig.

Enabling CONFIG_CRYPTO_DEV_S5P makes the system to resume without
any patches since the sss clock prevents aclk266_g2d to be gated.

But I wanted to know if it was really aclk266_g2d that was needed
or the actual sss clock since the kernel didn't manage that clock
without the driver enabled.

So I disabled the sss clock before trying a S2R:

# devmem 0x10018800 32 0xFFFFFFFB
(CLK_SSS in CLK_GATE_IP_G2D is gated)

and S2R worked anyways but I see that CLK_GATE_IP_G2D is reset to
its default value on S2R so maybe that is why it works anyways?

# devmem 0x10018800
0xFFFFFFFF (all CLK_GATE_IP_G2D clocks enabled including CLK_SSS)

Does this shed any more light? Could the problem be that the sss
clock parent (aclk266_g2d) is gated during S2R? Is the SSS module
required for S2R or is just that CLK_SSS prevents the parent to
be gated and so it is another red herring?

Best regards,
Javier