On Sat, 2013-08-03 at 04:24 +0800, Stephen Warren wrote: > On 08/02/2013 01:48 AM, Joseph Lo wrote: > > On Tue, 2013-07-30 at 06:47 +0800, Stephen Warren wrote: > >> On 07/26/2013 03:15 AM, Joseph Lo wrote: > >>> When suspending to LP1 mode, the SYSCLK will be clock gated. And different > >>> board may have different polarity of the request of SYSCLK, this patch > >>> configure the polarity from the DT for the board. > >> > >>> diff --git a/arch/arm/mach-tegra/pmc.c b/arch/arm/mach-tegra/pmc.c > >> > >>> @@ -238,6 +240,20 @@ void tegra_pmc_suspend_init(void) > >>> reg = tegra_pmc_readl(PMC_CTRL); > >>> reg |= TEGRA_POWER_CPU_PWRREQ_OE; > >>> tegra_pmc_writel(reg, PMC_CTRL); > >>> + > >>> + reg = tegra_pmc_readl(PMC_CTRL); > >>> + > >>> + if (!pmc_pm_data.sysclkreq_high) > >>> + reg |= TEGRA_POWER_SYSCLK_POLARITY; > >>> + else > >>> + reg &= ~TEGRA_POWER_SYSCLK_POLARITY; > >>> + > >>> + /* configure the output inverts while the request is tristated */ > >>> + tegra_pmc_writel(reg, PMC_CTRL); > >> > >> I think s/inverts/polarity/ in that comment would make a lot more sense. > >> > > Yes, thanks. > > > >> Must _OE be disabled for the code to work correctly? If so, should the > >> code explicitly clear _OE first, since who knows what state it was > >> originally in? Can't we just set the new polarity and enable _OE in a > >> single register write? > >> > > The SYSCLK is super clock that was connected to COP subsystem. It can't > > be disabled when system is running. The boot loader had initialized it > > and brought it to kernel. We follow the HW description in DT of the > > polarity of SCLK to re-configure and re-init again. Then the PMC can > > clock gate it when system go into suspend state. > > So it sounds like the bootloader has already configured the clock to a > certain polarity. If so, why do we need to reconfigure it again? > > Or, is this code not duplicating something the bootloader must have > done, but simply informing some HW in the PMC that's receiving SYSCLK > how the clock is configured elsewhere? I can't always guarantee the bootloader does the stuffs that kernel needs. For this reason, it's better to do what the kernel needs in the kernel. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
