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Thu, 09 Jan 2025 07:04:37 -0800 (PST) Date: Thu, 9 Jan 2025 10:04:34 -0500 From: Alan Stern To: Guan-Yu Lin Cc: gregkh@linuxfoundation.org, Thinh.Nguyen@synopsys.com, mathias.nyman@intel.com, perex@perex.cz, tiwai@suse.com, sumit.garg@linaro.org, kekrby@gmail.com, oneukum@suse.com, ricardo@marliere.net, lijiayi@kylinos.cn, quic_jjohnson@quicinc.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, linux-sound@vger.kernel.org Subject: Re: [PATCH v7 3/5] usb: add apis for offload usage tracking Message-ID: <69a4ae28-dbdc-48eb-b77b-147f58739913@rowland.harvard.edu> References: <20250109035605.1486717-1-guanyulin@google.com> <20250109035605.1486717-4-guanyulin@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250109035605.1486717-4-guanyulin@google.com> On Thu, Jan 09, 2025 at 03:55:07AM +0000, Guan-Yu Lin wrote: > Introduce offload_usage and corresponding apis to track offload usage > on each USB device. Offload denotes that there is another co-processor > accessing the USB device via the same USB host controller. To optimize > power usage, it's essential to monitor whether the USB device is > actively used by other co-processor. This information is vital when > determining if a USB device can be safely suspended during system power > state transitions. > > Signed-off-by: Guan-Yu Lin > --- > drivers/usb/core/driver.c | 108 ++++++++++++++++++++++++++++++++++++++ > drivers/usb/core/usb.c | 4 ++ > include/linux/usb.h | 19 +++++++ > 3 files changed, 131 insertions(+) > > diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c > index f203fdbfb6f6..01f6287cf73f 100644 > --- a/drivers/usb/core/driver.c > +++ b/drivers/usb/core/driver.c > @@ -2037,6 +2037,114 @@ int usb_disable_usb2_hardware_lpm(struct usb_device *udev) > > #endif /* CONFIG_PM */ > > +#ifdef CONFIG_USB_XHCI_SIDEBAND > + > +/** > + * usb_offload_get - increment the offload_usage of a USB device > + * @udev: the USB device to increment its offload_usage > + * > + * Incrementing the offload_usage of a usb_device indicates that offload is > + * enabled on this usb_device; that is, another entity is actively handling USB > + * transfers. This information allows the USB driver to adjust its power > + * management policy based on offload activity. > + * > + * The caller must hold @udev's device lock. > + * > + * Return: 0 on success. A negative error code otherwise. > + */ > +int usb_offload_get(struct usb_device *udev) > +{ > + int ret; > + > + if (udev->state == USB_STATE_NOTATTACHED || > + udev->state == USB_STATE_SUSPENDED) > + return -EAGAIN; > + > + /* > + * offload_usage could only be modified when the device is active, since > + * it will alter the suspend flow of the device. > + */ > + ret = pm_runtime_get_sync(&udev->dev); Note that this function will increment the runtime PM reference count even if it returns an error. You probably want to call pm_runtime_resume_and_get() instead. Likewise in usb_offload_put(). > + > + if (ret < 0) > + return ret; > + > + refcount_inc(&udev->offload_usage); > + pm_runtime_put_sync(&udev->dev); > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(usb_offload_get); Alan Stern