On 3/13/25 10:25, Philipp Zabel wrote: > On Do, 2025-03-06 at 17:43 +0100, Michal Wilczynski wrote: >> >> On 3/6/25 00:47, Stephen Boyd wrote: >>> Quoting Michal Wilczynski (2025-03-03 06:36:29) >>>> The T-HEAD TH1520 has three GPU clocks: core, cfg, and mem. The mem >>>> clock gate is marked as "Reserved" in hardware, while core and cfg are >>>> configurable. In order for these clock gates to work properly, the >>>> CLKGEN reset must be managed in a specific sequence. >>>> >>>> Move the CLKGEN reset handling to the clock driver since it's >>>> fundamentally a clock-related workaround [1]. This ensures that clk_enabled >>>> GPU clocks stay physically enabled without external interference from >>>> the reset driver. The reset is now deasserted only when both core and >>>> cfg clocks are enabled, and asserted when either of them is disabled. >>>> >>>> The mem clock is configured to use nop operations since it cannot be >>>> controlled. >>>> >>>> Link: https://lore.kernel.org/all/945fb7e913a9c3dcb40697328b7e9842b75fea5c.camel@xxxxxxxxxxxxxx [1] >>>> >>>> Signed-off-by: Michal Wilczynski <m.wilczynski@xxxxxxxxxxx> >>> [...] >>>> diff --git a/drivers/clk/thead/clk-th1520-ap.c b/drivers/clk/thead/clk-th1520-ap.c >>>> index ea96d007aecd..1dfcde867233 100644 >>>> --- a/drivers/clk/thead/clk-th1520-ap.c >>>> +++ b/drivers/clk/thead/clk-th1520-ap.c >>>> @@ -862,17 +863,70 @@ static CCU_GATE(CLK_SRAM1, sram1_clk, "sram1", axi_aclk_pd, 0x20c, BIT(3), 0); >>> [...] >>>> >>>> static CCU_GATE_CLK_OPS(CLK_GPU_MEM, gpu_mem_clk, "gpu-mem-clk", >>>> video_pll_clk_pd, 0x0, BIT(2), 0, clk_nop_ops); >>>> +static CCU_GATE_CLK_OPS(CLK_GPU_CORE, gpu_core_clk, "gpu-core-clk", >>>> + video_pll_clk_pd, 0x0, BIT(3), 0, ccu_gate_gpu_ops); >>>> +static CCU_GATE_CLK_OPS(CLK_GPU_CFG_ACLK, gpu_cfg_aclk, "gpu-cfg-aclk", >>>> + video_pll_clk_pd, 0x0, BIT(4), 0, ccu_gate_gpu_ops); >>>> + >>>> +static void ccu_gpu_clk_disable(struct clk_hw *hw) >>>> +{ >>>> + struct ccu_gate *cg = hw_to_ccu_gate(hw); >>>> + unsigned long flags; >>>> + >>>> + spin_lock_irqsave(&gpu_reset_lock, flags); >>>> + >>>> + ccu_disable_helper(&cg->common, cg->enable); >>>> + >>>> + if ((cg == &gpu_core_clk && >>>> + !clk_hw_is_enabled(&gpu_cfg_aclk.common.hw)) || >>>> + (cg == &gpu_cfg_aclk && >>>> + !clk_hw_is_enabled(&gpu_core_clk.common.hw))) >>>> + reset_control_assert(gpu_reset); >>> >>> Why can't the clk consumer control the reset itself? Doing this here is >>> not ideal because we hold the clk lock when we try to grab the reset >>> lock. These are all spinlocks that should be small in lines of code >>> where the lock is held, but we're calling into an entire other framework >>> under a spinlock. If an (unrelated) reset driver tries to grab the clk >>> lock it will deadlock. >> >> So in our case the clk consumer is the drm/imagination driver. Here is >> the comment from the maintainer for my previous attempt to use a reset >> driver to abstract the GPU init sequence [1]: >> >> "Do you know what this resets? From our side, the GPU only has a single >> reset line (which I assume to be GPU_RESET)." >> >> "I don't love that this procedure appears in the platform reset driver. >> I appreciate it may not be clear from the SoC TRM, but this is the >> standard reset procedure for all IMG Rogue GPUs. The currently >> supported TI SoC handles this in silicon, when power up/down requests >> are sent so we never needed to encode it in the driver before. >> >> Strictly speaking, the 32 cycle delay is required between power and >> clocks being enabled and the reset line being deasserted. If nothing >> here touches power or clocks (which I don't think it should), the delay >> could potentially be lifted to the GPU driver." >> >> From the drm/imagination maintainers point of view their hardware has >> only one reset, the extra CLKGEN reset is SoC specific. > > If I am understanding correctly, the CLKGEN reset doesn't reset > anything in the GPU itself, but holds the GPU clock generator block in > reset, effectively disabling the three GPU clocks as a workaround for > the always-ungated GPU_MEM clock. > >> Also the reset driver maintainer didn't like my way of abstracting two >> resets ("GPU" and and SoC specific"CLKGEN") into one reset > > That is one part of it. The other is that (according to my > understanding as laid out above), the combined GPU+CLKGEN reset would > effectively disable all three GPU clocks for a while, after the GPU > driver has already requested them to be enabled. Thank you for your comments Philipp, it seems like we're on the same page here. I was wondering whether there is anything I can do to move the patches forward. Stephen, if the current patch is a no go from your perspective could you please advise whether there is a way to solve this in a clock that would be acceptable to you. Thanks, Michał > >> to make it >> seem to the consumer driver drm/imagination like there is only one >> reset and suggested and attempt to code the re-setting in the clock >> driver [2]. Even though he suggested a different way of achieving that: >> >> "In my mind it shouldn't be much: the GPU clocks could all share the >> same refcounted implementation. The first clock to get enabled would >> ungate both GPU_CORE and GPU_CFG_ACLK gates and deassert >> GPU_SW_CLKGEN_RST, all in one place. The remaining enable(s) would be >> no-ops. Would that work?" >> >> The above would have similar effect, but I felt like enabling both >> clocks in single .enable callback could be confusing so I ended up with >> the current approach. This could be easily re-done if you feel this >> would be better. >> >> I agree that using spinlocks here is dangerous, but looking at the code >> of the reset_control_deassert and reset_control_assert, it doesn't seem >> like any spinlocks are acquired/relased in that code flow, unless the >> driver ops would introduce that. So in this specific case deadlock >> shouldn't happen ? > > There are no spinlocks in the reset_control_(de)assert paths in the > reset framework, but in general there could be in the driver. The thead > driver [1], uses regmap_update_bits() on a regmap with .fast_io = true, > which uses the internal struct regmap::spinlock. > > [1] https://lore.kernel.org/all/20250303152511.494405-3-m.wilczynski@xxxxxxxxxxx/ > > > regards > Philipp >
