Re: [PATCH 03/10] bus/fsl-mc: add support for 'driver_override' in the mc-bus

[Diana Craciun OSS]

On 3/23/2020 2:30 PM, Laurentiu Tudor wrote:
> On 3/19/2020 5:40 PM, Diana Craciun wrote:
> > From: Bharat Bhushan <Bharat.Bhushan@xxxxxxx>
> >
> > This patch is required for vfio-fsl-mc meta driver to successfully bind
> > layerscape container devices for device passthrough. This patch adds
> > a mechanism to allow a layerscape device to specify a driver rather than
> > a layerscape driver provide a device match.
> >
> > Example to allow a device (dprc.1) to specifically bind
> > with driver (vfio-fsl-mc):-
> >   - echo vfio-fsl-mc > /sys/bus/fsl-mc/devices/dprc.1/driver_override
> >   - echo dprc.1 > /sys/bus/fsl-mc/drivers/fsl_mc_dprc/unbind
> >   - echo dprc.1 > /sys/bus/fsl-mc/drivers/vfio-fsl-mc/bind
> >
> > Signed-off-by: Bharat Bhushan <Bharat.Bhushan@xxxxxxx>
> > Signed-off-by: Laurentiu Tudor <laurentiu.tudor@xxxxxxx>
> > Signed-off-by: Diana Craciun <diana.craciun@xxxxxxxxxxx>
> > ---
> >   drivers/bus/fsl-mc/fsl-mc-bus.c | 54 +++++++++++++++++++++++++++++++++
> >   include/linux/fsl/mc.h          |  1 +
> >   2 files changed, 55 insertions(+)
> >
> > diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
> > index c78d10ea641f..baf8259262a9 100644
> > --- a/drivers/bus/fsl-mc/fsl-mc-bus.c
> > +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
> > @@ -3,6 +3,7 @@
> >    * Freescale Management Complex (MC) bus driver
> >    *
> >    * Copyright (C) 2014-2016 Freescale Semiconductor, Inc.
> > + * Copyright 2019-2020 NXP
> >    * Author: German Rivera <German.Rivera@xxxxxxxxxxxxx>
> >    *
> >    */
> > @@ -83,6 +84,12 @@ static int fsl_mc_bus_match(struct device *dev, struct device_driver *drv)
> >   	struct fsl_mc_driver *mc_drv = to_fsl_mc_driver(drv);
> >   	bool found = false;
> >   
> > +	/* When driver_override is set, only bind to the matching driver */
> > +	if (mc_dev->driver_override) {
> > +		found = !strcmp(mc_dev->driver_override, mc_drv->driver.name);
> I think we can use sysfs_streq() here and ...

I would prefer to maintain consistency with other buses and store the 
driver_override string without the terminating newline.

> > +		goto out;
> > +	}
> > +
> >   	if (!mc_drv->match_id_table)
> >   		goto out;
> >   
> > @@ -147,8 +154,52 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
> >   }
> >   static DEVICE_ATTR_RO(modalias);
> >   
> > +static ssize_t driver_override_store(struct device *dev,
> > +				     struct device_attribute *attr,
> > +				     const char *buf, size_t count)
> > +{
> > +	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
> > +	const char *driver_override, *old = mc_dev->driver_override;
> > +	char *cp;
> > +
> > +	if (WARN_ON(dev->bus != &fsl_mc_bus_type))
> > +		return -EINVAL;
> > +
> > +	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';
> drop this strchr() ...
>
> > +	if (strlen(driver_override)) {
> > +		mc_dev->driver_override = driver_override;
> > +	} else {
> > +		kfree(driver_override);
> > +		mc_dev->driver_override = NULL;
> > +	}
> > +
> > +	kfree(old);
> > +
> > +	return count;
> > +}
> > +
> > +static ssize_t driver_override_show(struct device *dev,
> > +				    struct device_attribute *attr, char *buf)
> > +{
> > +	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
> > +
> > +	return snprintf(buf, PAGE_SIZE, "%s\n", mc_dev->driver_override);
> and also the terminating '\n' here.
>
> > +}
> > +static DEVICE_ATTR_RW(driver_override);
> > +
> >   static struct attribute *fsl_mc_dev_attrs[] = {
> >   	&dev_attr_modalias.attr,
> > +	&dev_attr_driver_override.attr,
> >   	NULL,
> >   };
> >   
> > @@ -704,6 +755,9 @@ EXPORT_SYMBOL_GPL(fsl_mc_device_add);
> >    */
> >   void fsl_mc_device_remove(struct fsl_mc_device *mc_dev)
> >   {
> > +	kfree(mc_dev->driver_override);
> > +	mc_dev->driver_override = NULL;
> > +
> >   	/*
> >   	 * The device-specific remove callback will get invoked by device_del()
> >   	 */
> > diff --git a/include/linux/fsl/mc.h b/include/linux/fsl/mc.h
> > index 54d9436600c7..88095fd30c80 100644
> > --- a/include/linux/fsl/mc.h
> > +++ b/include/linux/fsl/mc.h
> > @@ -194,6 +194,7 @@ struct fsl_mc_device {
> >   	struct fsl_mc_device_irq **irqs;
> >   	struct fsl_mc_resource *resource;
> >   	struct device_link *consumer_link;
> > +	const char *driver_override;
> We probably don't want const here.

OK

> ---
> Best Regards, Laurentiu
>
> >   };
> >   
> >   #define to_fsl_mc_device(_dev) \

Diana