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

[Laurentiu Tudor <laurentiu.tudor@nxp.com>]

On 3/19/2020 5:40 PM, Diana Craciun wrote:
> From: Bharat Bhushan <Bharat.Bhushan@nxp.com>
> 
> 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@nxp.com>
> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
> Signed-off-by: Diana Craciun <diana.craciun@oss.nxp.com>
> ---
>  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@freescale.com>
>   *
>   */
> @@ -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 ...


> +		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.

---
Best Regards, Laurentiu

>  };
>  
>  #define to_fsl_mc_device(_dev) \
>