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Date: Mon, 19 Oct 2020 07:46:23 +0000
From: "Wu, Hao" <hao.wu@...el.com>
To: "Xu, Yilun" <yilun.xu@...el.com>, Tom Rix <trix@...hat.com>
CC: "mdf@...nel.org" <mdf@...nel.org>,
"linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"lgoncalv@...hat.com" <lgoncalv@...hat.com>
Subject: RE: [PATCH 1/2] fpga: dfl: add driver_override support
> On Fri, Oct 16, 2020 at 09:21:50AM -0700, Tom Rix wrote:
> >
> > On 10/15/20 11:02 PM, Xu Yilun wrote:
> > > Add support for overriding the default matching of a dfl device to a dfl
> > > driver. It follows the same way that can be used for PCI and platform
> > > devices. This patch adds the 'driver_override' sysfs file.
> > >
> > > Signed-off-by: Xu Yilun <yilun.xu@...el.com>
> > > ---
> > > Documentation/ABI/testing/sysfs-bus-dfl | 28 ++++++++++++++---
> > > drivers/fpga/dfl.c | 54
> ++++++++++++++++++++++++++++++++-
> > > include/linux/dfl.h | 2 ++
> > > 3 files changed, 79 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-bus-dfl
> b/Documentation/ABI/testing/sysfs-bus-dfl
> > > index 23543be..db7e8d3 100644
> > > --- a/Documentation/ABI/testing/sysfs-bus-dfl
> > > +++ b/Documentation/ABI/testing/sysfs-bus-dfl
> > > @@ -1,15 +1,35 @@
> > > What: /sys/bus/dfl/devices/dfl_dev.X/type
> > > -Date: Aug 2020
> > > -KernelVersion: 5.10
> > > +Date: Oct 2020
> > > +KernelVersion: 5.11
> > > Contact: Xu Yilun <yilun.xu@...el.com>
> > > Description: Read-only. It returns type of DFL FIU of the device.
> Now DFL
> > > supports 2 FIU types, 0 for FME, 1 for PORT.
> > > Format: 0x%x
> > >
> > > What: /sys/bus/dfl/devices/dfl_dev.X/feature_id
> > > -Date: Aug 2020
> > > -KernelVersion: 5.10
> > > +Date: Oct 2020
> > > +KernelVersion: 5.11
> > > Contact: Xu Yilun <yilun.xu@...el.com>
> > > Description: Read-only. It returns feature identifier local to its DFL
> FIU
> > > type.
> > > Format: 0x%x
> >
> > These updates, do not match the comment.
> >
> > Consider splitting this out.
>
> I'm sorry it's a typo. The above code should not be changed.
>
> >
> > > +
> > > +What: /sys/bus/dfl/devices/.../driver_override
> > > +Date: Oct 2020
> > > +KernelVersion: 5.11
> > > +Contact: Xu Yilun <yilun.xu@...el.com>
> > I am looking at description and trying to make it consistent with sysfs-bus-
> pci
> > > +Description: This file allows the driver for a device to be specified.
> >
> > 'to be specified which will override the standard dfl bus feature id to driver
> mapping.'
>
> Yes, it could be improved.
>
> Actually now it is the "type" and "feature id" matching, the 2 fields
> are defined for dfl_driver.id_table. In future for dfl v1, it may be
> GUID matching, which will be added to id_table. So how about we make it
> more generic:
>
> 'to be specified which will override the standard ID table matching.'
>
> >
> >
> > > When
> > > + specified, only a driver with a name matching the value written
> > > + to driver_override will have an opportunity to bind to the
> > > + device. The override is specified by writing a string to the
> > > + driver_override file (echo dfl-uio-pdev > driver_override) and
> > > + may be cleared with an empty string (echo > driver_override).
> > > + This returns the device to standard matching rules binding.
> > > + Writing to driver_override does not automatically unbind the
> > > + device from its current driver or make any attempt to
> > > + automatically load the specified driver. If no driver with a
> > > + matching name is currently loaded in the kernel, the device
> > > + will not bind to any driver. This also allows devices to
> > > + opt-out of driver binding using a driver_override name such as
> > > + "none". Only a single driver may be specified in the override,
> > > + there is no support for parsing delimiters.
> > > diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c
> > > index 511b20f..bc35750 100644
> > > --- a/drivers/fpga/dfl.c
> > > +++ b/drivers/fpga/dfl.c
> > > @@ -262,6 +262,10 @@ static int dfl_bus_match(struct device *dev,
> struct device_driver *drv)
> > > struct dfl_driver *ddrv = to_dfl_drv(drv);
> > > const struct dfl_device_id *id_entry;
> > >
> > > + /* When driver_override is set, only bind to the matching driver */
> > > + if (ddev->driver_override)
> > > + return !strcmp(ddev->driver_override, drv->name);
> > > +
> > > id_entry = ddrv->id_table;
> > > if (id_entry) {
> > > while (id_entry->feature_id) {
> > > @@ -303,6 +307,53 @@ static int dfl_bus_uevent(struct device *dev,
> struct kobj_uevent_env *env)
> > > ddev->type, ddev->feature_id);
> > > }
> > >
> >
> > I am looking at other implementations of driver_override* and looking for
> consistency.
> >
> > > +static ssize_t driver_override_show(struct device *dev,
> > > + struct device_attribute *attr, char *buf)
> > > +{
> > > + struct dfl_device *ddev = to_dfl_dev(dev);
> > > + ssize_t len;
> > > +
> > > + device_lock(dev);
> > > + len = sprintf(buf, "%s\n", ddev->driver_override);
> > len = snprintf(buf, PAGE_SIZE ...
>
> It is good to me.
>
> Some bus drivers use snprintf, some use sprintf.
>
> I think it is reasonable snprintf is used here, unlike %d, %u ... it is
> uncertain for the output size of %s.
you limited the size < a page in store function for driver_override?
Hao
>
> > > + device_unlock(dev);
> > > + return len;
> > > +}
> > > +
> > > +static ssize_t driver_override_store(struct device *dev,
> > > + struct device_attribute *attr,
> > > + const char *buf, size_t count)
> > > +{
> > > + struct dfl_device *ddev = to_dfl_dev(dev);
> > > + char *driver_override, *old, *cp;
> > > +
> > > + /* We need to keep extra room for a newline */
> > > + if (count >= (PAGE_SIZE - 1))
> > > + return -EINVAL;
> > > +
> > > + driver_override = kstrndup(buf, count, GFP_KERNEL);
> > > + if (!driver_override)
> > > + return -ENOMEM;
> > > +
> > > + cp = strchr(driver_override, '\n');
> > > + if (cp)
> > > + *cp = '\0';
> > > +
> > > + device_lock(dev);
> > > + old = ddev->driver_override;
> > > + if (strlen(driver_override)) {
> > > + ddev->driver_override = driver_override;
> > > + } else {
> > > + kfree(driver_override);
> > > + ddev->driver_override = NULL;
> > > + }
> > > + device_unlock(dev);
> > > +
> > > + kfree(old);
> > > +
> > > + return count;
> > > +}
> > > +static DEVICE_ATTR_RW(driver_override);
> > > +
> > > static ssize_t
> > > type_show(struct device *dev, struct device_attribute *attr, char *buf)
> > > {
> > > @@ -324,6 +375,7 @@ static DEVICE_ATTR_RO(feature_id);
> > > static struct attribute *dfl_dev_attrs[] = {
> > > &dev_attr_type.attr,
> > > &dev_attr_feature_id.attr,
> > > + &dev_attr_driver_override.attr,
> > > NULL,
> > > };
> > > ATTRIBUTE_GROUPS(dfl_dev);
> > > @@ -469,7 +521,7 @@ static int dfl_devs_add(struct
> dfl_feature_platform_data *pdata)
> > >
> > > int __dfl_driver_register(struct dfl_driver *dfl_drv, struct module *owner)
> > > {
> > > - if (!dfl_drv || !dfl_drv->probe || !dfl_drv->id_table)
> > > + if (!dfl_drv || !dfl_drv->probe)
> >
> > id_table is still needed for the normal case.
> >
> > Instead of removing this check, could you add something like
> >
> > || (!dfl_drv->is_override && !dfl_drv->id_table)
>
> I don't think it is needed. Seems is_override and !id_table are duplicated
> conditions for this implementation. And it may make confusing, e.g. could
> a driver been force matched when is_override is not set?
>
> I think we could make it simple, if the dfl driver didn't provide the
> id_table, normally it could not match any device. I think it could be
> easily understood by dfl driver developers.
>
>
> Thanks,
> Yilun
>
> >
> > Tom
> >
> > > return -EINVAL;
> > >
> > > dfl_drv->drv.owner = owner;
> > > diff --git a/include/linux/dfl.h b/include/linux/dfl.h
> > > index 7affba2f..e1b2471 100644
> > > --- a/include/linux/dfl.h
> > > +++ b/include/linux/dfl.h
> > > @@ -32,6 +32,7 @@ enum dfl_id_type {
> > > * @num_irqs: number of IRQs supported by this dfl device.
> > > * @cdev: pointer to DFL FPGA container device this dfl device belongs to.
> > > * @id_entry: matched id entry in dfl driver's id table.
> > > + * @driver_override: driver name to force a match
> > > */
> > > struct dfl_device {
> > > struct device dev;
> > > @@ -43,6 +44,7 @@ struct dfl_device {
> > > unsigned int num_irqs;
> > > struct dfl_fpga_cdev *cdev;
> > > const struct dfl_device_id *id_entry;
> > > + char *driver_override;
> > > };
> > >
> > > /**
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