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Mon, 08 Sep 2025 06:06:52 -0700 (PDT) Message-ID: <742cf1ae-1723-4cf5-8931-afd35699cc95@tuxon.dev> Date: Mon, 8 Sep 2025 16:06:50 +0300 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 5/9] PCI: rzg3s-host: Add Initial PCIe Host Driver for Renesas RZ/G3S SoC To: Manivannan Sadhasivam , Geert Uytterhoeven Cc: bhelgaas@google.com, lpieralisi@kernel.org, kwilczynski@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, magnus.damm@gmail.com, catalin.marinas@arm.com, will@kernel.org, mturquette@baylibre.com, sboyd@kernel.org, p.zabel@pengutronix.de, lizhi.hou@amd.com, linux-pci@vger.kernel.org, linux-renesas-soc@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org, Claudiu Beznea , Wolfram Sang References: <20250704161410.3931884-1-claudiu.beznea.uj@bp.renesas.com> <20250704161410.3931884-6-claudiu.beznea.uj@bp.renesas.com> <8ef466aa-b470-4dcb-9024-0a9c36eb9a6a@tuxon.dev> <6f2hpdkonomgrfzqoupcex2rpqtlhql4lmsqm7hqk25qakp7ax@bfrzflghmnev> From: Claudiu Beznea Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, Manivannan, On 9/1/25 18:54, Manivannan Sadhasivam wrote: > On Mon, Sep 01, 2025 at 04:22:16PM GMT, Geert Uytterhoeven wrote: >> Hi Mani, >> >> On Mon, 1 Sept 2025 at 16:04, Manivannan Sadhasivam wrote: >>> On Mon, Sep 01, 2025 at 11:25:30AM GMT, Geert Uytterhoeven wrote: >>>> On Sun, 31 Aug 2025 at 06:07, Manivannan Sadhasivam wrote: >>>>> On Sat, Aug 30, 2025 at 02:22:45PM GMT, Claudiu Beznea wrote: >>>>>> On 30.08.2025 09:59, Manivannan Sadhasivam wrote: >>>>>>> On Fri, Jul 04, 2025 at 07:14:05PM GMT, Claudiu wrote: >>>>>>>> From: Claudiu Beznea >>>>>>>> >>>>>>>> The Renesas RZ/G3S features a PCIe IP that complies with the PCI Express >>>>>>>> Base Specification 4.0 and supports speeds of up to 5 GT/s. It functions >>>>>>>> only as a root complex, with a single-lane (x1) configuration. The >>>>>>>> controller includes Type 1 configuration registers, as well as IP >>>>>>>> specific registers (called AXI registers) required for various adjustments. >>>>>>>> >>>>>>>> Hardware manual can be downloaded from the address in the "Link" section. >>>>>>>> The following steps should be followed to access the manual: >>>>>>>> 1/ Click the "User Manual" button >>>>>>>> 2/ Click "Confirm"; this will start downloading an archive >>>>>>>> 3/ Open the downloaded archive >>>>>>>> 4/ Navigate to r01uh1014ej*-rzg3s-users-manual-hardware -> Deliverables >>>>>>>> 5/ Open the file r01uh1014ej*-rzg3s.pdf >>>>>>>> >>>>>>>> Link: https://www.renesas.com/en/products/rz-g3s?queryID=695cc067c2d89e3f271d43656ede4d12 >>>>>>>> Tested-by: Wolfram Sang >>>>>>>> Signed-off-by: Claudiu Beznea >>>> >>>>>>>> + ret = pm_runtime_resume_and_get(dev); >>>>>>>> + if (ret) >>>>>>>> + return ret; >>>>>>>> + >>>>>>> >>>>>>> Do you really need to do resume_and_get()? If not, you should do: >>>>>> >>>>>> It it's needed to enable the clock PM domain the device is part of. >>>>>> >>>>> >>>>> I've replied below. >>>>> >>>>>>> >>>>>>> pm_runtime_set_active() >>>>>>> pm_runtime_no_callbacks() >>>>>>> devm_pm_runtime_enable() >>>> >>>>>>>> +static int rzg3s_pcie_suspend_noirq(struct device *dev) >>>>>>>> +{ >>>>>>>> + struct rzg3s_pcie_host *host = dev_get_drvdata(dev); >>>>>>>> + const struct rzg3s_pcie_soc_data *data = host->data; >>>>>>>> + struct regmap *sysc = host->sysc; >>>>>>>> + int ret; >>>>>>>> + >>>>>>>> + ret = pm_runtime_put_sync(dev); >>>>>>>> + if (ret) >>>>>>>> + return ret; >>>>>>> >>>>>>> Since there are no runtime callbacks present, managing runtime PM in the driver >>>>>>> makes no sense. >>>>>> >>>>>> The PCIe device is part of a clock power domain. Dropping >>>>>> pm_runtime_enable()/pm_runtime_put_sync() in this driver will lead to this >>>>>> IP failing to work as its clocks will not be enabled/disabled. If you don't >>>>>> like the pm_runtime_* approach that could be replaced with: >>>>>> >>>>>> devm_clk_get_enabled() in probe and clk_disable()/clk_enable() on >>>>>> suspend/resume. W/o clocks the IP can't work. >>>>> >>>>> Yes, you should explicitly handle clocks in the driver. Runtime PM makes sense >>>>> if you have a power domain attached to the IP, which you also do as I see now. >>>>> So to conclude, you should enable/disable the clocks explicitly for managing >>>>> clocks and use runtime PM APIs for managing the power domain associated with >>>>> clock controller. >>>> >>>> Why? For the past decade, we've been trying to get rid of explicit >>>> module clock handling for all devices that are always part of a >>>> clock domain. >>>> >>>> The Linux PM Domain abstraction is meant for both power and clock >>>> domains. This is especially useful when a device is present on multiple >>>> SoCs, on some also part of a power domain, and the number of module >>>> clocks that needs to be enabled for it to function is not the same on >>>> all SoCs. In such cases, the PM Domain abstraction takes care of many >>>> of the integration-specific differences. >>> >>> Hmm, my understanding was that we need to explicitly handle clocks from the >>> consumer drivers. But that maybe because, the client drivers I've dealt with >>> requires configuring the clocks (like setting the rate, re-parenting etc...) on >>> their own. But if there is no such requirement, then I guess it is OK to rely on >>> the PM core and clock controller drivers. >> >> When you need to know the actual clock rate, or change it, you >> indeed have to handle the clock explicitly. But it still may be enabled >> automatically through the clock domain. >> > > Yeah! > >>>>> But please add a comment above pm_runtime_resume_and_get() to make it clear as >>>>> most of the controller drivers are calling it for no reason. >>>> >>>> Note that any child device that uses Runtime PM depends on all >>>> its parents in the hierarchy to call pm_runtime_enable() and >>>> pm_runtime_resume_and_get(). >>> >>> Two things to note from your statement: >>> >>> 1. 'child device that uses runtime PM' - Not all child drivers are doing >>> runtime PM on their own. So there is no need to do pm_runtime_resume_and_get() >>> unless they depend on the parent for resource enablement as below. >> >> It indeed depends on the child device, and on the bus. For e.g. an >> Ethernet controller connected to a simple SoC expansion bus, the bus must >> be powered and clock, which is what "simple-pm-bus" takes care of >> ("simple-bus" does not). >> > > Right. But most of the PCI controller drivers call pm_runtime_resume_and_get() > for no good reasons. They might have just copied the code from a driver that did > it on purpose. So I tend to scrutinize these calls whenever they get added for a > driver. To be sure I will prepare the next version with something that was requested: are you OK with keeping pm_runtime_resume_and_get() and add a comment for it? Thank you, Claudiu