Hello Sylwester, On 04/01/2015 01:03 PM, Sylwester Nawrocki wrote: > > On 31/03/15 22:00, Javier Martinez Canillas wrote: >> On 03/31/2015 04:38 PM, Abhilash Kesavan wrote: >>> javier.martinez@xxxxxxxxxxxxxxx> wrote: > >>>> Unfortunately I don't fully understand why this clock needs to be >>>> enabled. It would be good if someone at Samsung can explain in >>>> more detail what the real problem really is. >>>> >>> >>> I had a look at this some more today. The problem actually occurs when the >>> mdma0 clock's parent - aclk266_g2d gets disabled. The run-time pm support >>> in the dma driver disables mdma0 and in turn aclk266_g2d which causes the >>> issue. >>> From the User Manual, it appears that aclk266_g2d should be gated only when >>> certain bits in the clock gating status register are 0. I cannot say for >>> certain, but our gating the aclk266_g2d clock without the CG_STATUS bits >>> being 0 could be a cause of the suspend failure. >>> >> >> Thanks a lot for the explanation. I see the NOTE at the bottom of section >> 7.9.1.159 CLK_GATE_BUS_TOP that mentions that. I'll add this information >> to the commit message when posting as a proper patch instead of a RFC. >> >> I confirmed that changing the patch to prevent "aclk266_g2d" to be gated >> instead of "mdm0" also makes the system to resume correctly from suspend >> so I'll change that on the patch as well. >> >> I see that many of the Exynos5420 clocks (including "aclk266_g2d") use the >> CLK_IGNORE_UNUSED flag but AFAIU it only prevents the common clock framework >> to disable the clocks on init but doesn't prevent the clocks to be disabled >> if all the clock childs are gated so the parent is gated as well. >> >>> As the CG_STATUS bits are not being checked anywhere in the kernel I think >>> aclk266_g2d (and others in GATE_BUS_TOP) should not be gated. I am OK with >> >> For now I'll just add "aclk266_g2d" but later if needed all the GATE_BUS_TOP >> clocks (and others) that should only be gated when CG_STATUS is 0 can be >> added. My patch iterates over a list of clocks to be kept during suspend even >> when there is only one for now so adding more later if needed will be trivial. > > It's not clear what subsystems affect state of the CG_STATUSx registers, it > would be good if we could get more information on that. They are in the PMU > block and are related to LPI (Low Power Interface handshaking), but what > subsystems/peripheral blocks exactly are associated with them it's not clear > from the documentation. > Yes, I've been looking at the docs again and found out a couple of things: * Each GC_STATUSx register bit is associated with an IP hw block * Some LPI_MASKx registers maps exactly with the GC_STATUSx (i.e: 0 and 1) and others maps only partially (i.e: LPI_MASK2 and GC_STATUS2) So it is related to LPI as you said and both LPI_MASKx and GC_STATUSx are part of the PMU register address space. In the particular case of aclk266_g2d, the doc says that the clock can only be gated when CG_STATUS0[20] and CG_STATUS0[21] are 0. These are associated with the SSS and SSS_SLIM respectively which AFAIU are crypto h/w modules. > I think it's essential to understand what triggers changes in CG_STATUSx > registers, before we start checking their value in the clock driver. > Indeed, we should really understand what the status on these registers means. Also is not clear from the docs how much time should be waited, how long until giving up, etc. > Also it might be that there are indeed some clocks which must stay enabled > over suspend/resume cycle, then the approach with enabling/disabling clocks > in the clock driver might not be such a hack as it looks at first sight. > Having a clock driver to both a provider and consumer feels hacky to me as well but I didn't find a better way to solve this issue... another option is to have this workaround to solve the S2R issue while we figure out what the the state in the CG_STATUSx really mean. >> Or do you think that I should add all the GATE_BUS_TOP clocks now? > > No, please don't do that. That includes many important clocks and we should > be certain what we are doing. I don't think it is expected to touch those > clocks in that way, it would likely cause more issues. > > Perfect, I just asked since it was not clear to me from Abhilash comment. But I also agree to only focus on the clock that is causing issues now. Best regards, Javier -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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