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Sat, 09 May 2020 09:37:11 -0700 (PDT) Subject: Re: [PATCH] usb: roles: Switch on role-switch uevent reporting To: Wen Yang , heikki.krogerus@linux.intel.com, gregkh@linuxfoundation.org, linux-usb@vger.kernel.org Cc: Chunfeng Yun , Suzuki K Poulose , Alexandre Belloni , chenqiwu , linux-kernel@vger.kernel.org References: <20200508162937.2566818-1-bryan.odonoghue@linaro.org> From: Bryan O'Donoghue Message-ID: <10ca119e-ff09-70e7-311d-420aba612df6@linaro.org> Date: Sat, 9 May 2020 17:37:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/2020 04:24, Wen Yang wrote: > > > 在 2020/5/9 上午12:29, Bryan O'Donoghue 写道: >> Right now we don't report to user-space a role switch when doing a >> usb_role_switch_set_role() despite having registered the uevent >> callbacks. >> >> This patch switches on the notifications allowing user-space to see >> role-switch change notifications and subsequently determine the current >> controller data-role. >> >> example: >> PFX=/devices/platform/soc/78d9000.usb/ci_hdrc.0 >> >> root@somebox# udevadm monitor -p >> >> KERNEL[49.894994] change $PFX/usb_role/ci_hdrc.0-role-switch (usb_role) >> ACTION=change >> DEVPATH=$PFX/usb_role/ci_hdrc.0-role-switch >> SUBSYSTEM=usb_role >> DEVTYPE=usb_role_switch >> USB_ROLE_SWITCH=ci_hdrc.0-role-switch >> SEQNUM=2432 >> >> Cc: Heikki Krogerus >> Cc: Greg Kroah-Hartman >> Cc: Chunfeng Yun >> Cc: Suzuki K Poulose >> Cc: Alexandre Belloni >> Cc: Wen Yang >> Cc: chenqiwu >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Bryan O'Donoghue >> --- >>   drivers/usb/roles/class.c | 4 +++- >>   1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c >> index 5b17709821df..27d92af29635 100644 >> --- a/drivers/usb/roles/class.c >> +++ b/drivers/usb/roles/class.c >> @@ -49,8 +49,10 @@ int usb_role_switch_set_role(struct usb_role_switch >> *sw, enum usb_role role) >>       mutex_lock(&sw->lock); >>       ret = sw->set(sw, role); >> -    if (!ret) >> +    if (!ret) { >>           sw->role = role; >> +        kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE); >> +    } >>       mutex_unlock(&sw->lock); >> > > Hi, we may also need to deal with the return value of kobject_uevent(). For an KOBJ_ADD you'd return an error. grep -r "= kobject_uevent(" * drivers/misc/cxl/sysfs.c: rc = kobject_uevent(&cr->kobj, KOBJ_ADD); drivers/uio/uio.c: ret = kobject_uevent(&map->kobj, KOBJ_ADD); drivers/uio/uio.c: ret = kobject_uevent(&portio->kobj, KOBJ_ADD); drivers/visorbus/visorchipset.c: res = kobject_uevent(&chipset_dev->acpi_device->dev.kobj, KOBJ_ONLINE); drivers/visorbus/visorchipset.c: int res = kobject_uevent(&chipset_dev->acpi_device->dev.kobj, For a KOBJ_CHANGE I guess we could print an error if (kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE) dev_err(&sw->dev, "failed to signal USB role-switch uevent\n"); Nobody else seems that bothered about it. grep -r "if (kobject_uevent(" * > Should we move it under the line mutex_unlock(&sw->lock)? I think probably not. the mutex serializes the notification. In theory outside the mutex you could get an out-of-order notification. The main reason I put it where it is, is we already test ret and should only notify the change, when the role-switch has suceeded. As I say, in theory anyway, the mutex enforces the signalling, whatever about the reception, of the role-switch change, so IMO inside the bounds of the mutex is the right place to put it. --- bod