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Subject: Re: [PATCH 03/10] bus/fsl-mc: add support for 'driver_override' in
 the mc-bus
To:     Laurentiu Tudor <laurentiu.tudor@nxp.com>,
        linux-kernel@vger.kernel.org, stuyoder@gmail.com,
        leoyang.li@nxp.com, linux-arm-kernel@lists.infradead.org,
        bharatb.yadav@gmail.com
Cc:     Bharat Bhushan <Bharat.Bhushan@nxp.com>
References: <20200319154051.30609-1-diana.craciun@oss.nxp.com>
 <20200319154051.30609-4-diana.craciun@oss.nxp.com>
 <99ef2746-6be8-5427-26af-0a34c17f8fd2@nxp.com>
From:   Diana Craciun OSS <diana.craciun@oss.nxp.com>
Message-ID: <a0af9de5-a234-dbd6-1365-29a1e19ee1aa@oss.nxp.com>
Date:   Thu, 9 Apr 2020 14:14:20 +0300
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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@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 ...

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