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R. Silva" , Chia-I Wu , Chen-Yu Tsai , AngeloGioacchino Del Regno Cc: kernel@collabora.com, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-pm@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2 10/10] drm/panthor: add support for MediaTek MFlexGraphics Date: Mon, 15 Sep 2025 15:32:23 +0200 Message-ID: <117198807.nniJfEyVGO@workhorse> In-Reply-To: References: <20250912-mt8196-gpufreq-v2-0-779a8a3729d9@collabora.com> <20250912-mt8196-gpufreq-v2-10-779a8a3729d9@collabora.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250915_063428_304939_1F22AE4C X-CRM114-Status: GOOD ( 43.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Monday, 15 September 2025 12:28:09 Central European Summer Time AngeloGioacchino Del Regno wrote: > Il 12/09/25 20:37, Nicolas Frattaroli ha scritto: > > MediaTek uses some glue logic to control frequency and power on some of > > their GPUs. This is best exposed as a devfreq driver, as it saves us > > from having to hardcode OPPs into the device tree, and can be extended > > with additional devfreq-y logic like more clever governors that use the > > hardware's GPUEB MCU to set frame time targets and power limits. > > > > Add this driver to the panthor subdirectory. It needs to live here as it > > needs to call into panthor's devfreq layer, and panthor for its part > > also needs to call into this driver during probe to get a devfreq device > > registered. Solving the cyclical dependency by having mediatek_mfg live > > without knowledge of what a panthor is would require moving the devfreq > > provider stuff into a generic devfreq subsystem solution, which I didn't > > want to do. > > > > Signed-off-by: Nicolas Frattaroli > > --- > > drivers/gpu/drm/panthor/Kconfig | 13 + > > drivers/gpu/drm/panthor/Makefile | 2 + > > drivers/gpu/drm/panthor/mediatek_mfg.c | 1053 ++++++++++++++++++++++++++++++++ > > 3 files changed, 1068 insertions(+) > > > [ ... snip ...] > > +static int mtk_mfg_eb_on(struct mtk_mfg *mfg) > > +{ > > + struct device *dev = &mfg->pdev->dev; > > + u32 val; > > + int ret; > > + > > + /* > > + * If MFG is already on from e.g. the bootloader, we should skip doing > > + * the power-on sequence, as it wouldn't work without powering it off > > + * first. > > + */ > > + if ((readl(mfg->rpc + RPC_PWR_CON) & PWR_ACK_M) == PWR_ACK_M) > > + return 0; > > + > > + ret = readl_poll_timeout(mfg->rpc + RPC_GHPM_RO0_CON, val, > > + !(val & (GHPM_PWR_STATE_M | GHPM_STATE_M)), > > + GPUEB_POLL_US, GPUEB_TIMEOUT_US); > > + if (ret) { > > + dev_err(dev, "timed out waiting for EB to power on\n"); > > + return ret; > > + } > > + > > + mtk_mfg_update_reg_bits(mfg->rpc + mfg->ghpm_en_reg, GHPM_ENABLE_M, > > + GHPM_ENABLE_M); > > + > > + mtk_mfg_update_reg_bits(mfg->rpc + RPC_GHPM_CFG0_CON, GHPM_ON_SEQ_M, 0); > > + mtk_mfg_update_reg_bits(mfg->rpc + RPC_GHPM_CFG0_CON, GHPM_ON_SEQ_M, > > + GHPM_ON_SEQ_M); > > + > > + mtk_mfg_update_reg_bits(mfg->rpc + mfg->ghpm_en_reg, GHPM_ENABLE_M, 0); > > + > > + > > + ret = readl_poll_timeout(mfg->rpc + RPC_PWR_CON, val, > > + (val & PWR_ACK_M) == PWR_ACK_M, > > + GPUEB_POLL_US, GPUEB_TIMEOUT_US); > > I wonder if you can check how much time does the GPUEB really take to poweron, > just so that we might be able to reduce delay_us here. I already did, that's where the 50us value is from as far as I remember. > > > + if (ret) { > > + dev_err(dev, "timed out waiting for EB power ack, val = 0x%X\n", > > + val); > > + return ret; > > + } > > + > > + ret = readl_poll_timeout(mfg->gpr + GPR_LP_STATE, val, > > + (val == EB_ON_RESUME), > > + GPUEB_POLL_US, GPUEB_TIMEOUT_US); > > Same here - and I think this one is more critical, as I can see this suspend/resume > control being used more extensively in the future. > > Specifically, I'm wondering if we could add runtime PM ops that will request EB > suspend/resume - and also if doing so would make any sense. > > I am guessing that the "suspend" LP_STATE stops the internal state machine, making > the EB MCU to either go in a low-power state or to anyway lower its power usage by > at least suspending the iterations. I think I briefly fiddled with this but then it did nothing other than break everything. Is the current time it takes to resume a problem? > > Of course - here I mean that we could have > 1. System suspend ops that powers off the EB completely like you're doing here and > 2. Runtime PM op that may be called (very) aggressively > > ...this would obviously not be feasible if the EB suspend/resume (without complete > poweron/off) takes too much time to actually happen. We probably don't want to aggressively suspend the thing doing DVFS while a workload is running, and if no workload is running, it already suspends. I can't really say how normal desktop usage will play out yet, but generally speaking I think it's a bit early to find a comfortable place on the transition latency vs power draw curve at this point. > [... snip ...] > > +static int mtk_mfg_init_shared_mem(struct mtk_mfg *mfg) > > +{ > > [... snip ...] > > + > > + dev_info(dev, "initialised mem at phys 0x%016llX\n", mfg->sram_phys); > > I don't like exposing addresses in kmsg. Please just don't. It's a physical address. This is not a kernel pointer, but something that can be read from the DTS. But sure, I'll remove it I guess? > [... snip ...] > > Cheers, > Angelo > You can assume me not responding to a part of the feedback in this e-mail means I'll address it in the next revision of the patch series. Kind regards, Nicolas Frattaroli