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Subject: Re: [RFC PATCH 1/5] fsi/scom: Add mutex around FSI2PIB accesses
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        openbmc@lists.ozlabs.org
Cc:     Andrew Jeffery <andrew@aj.id.au>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
References: <20180612051911.20690-1-benh@kernel.crashing.org>
 <20180612051911.20690-2-benh@kernel.crashing.org>
From:   Eddie James <eajames@linux.vnet.ibm.com>
Date:   Wed, 13 Jun 2018 09:59:01 -0500
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On 06/12/2018 12:19 AM, Benjamin Herrenschmidt wrote:
> Otherwise, multiple clients can open the driver and attempt
> to access the PIB at the same time, thus clobbering each other
> in the process.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Reviewed-by: Eddie James <eajames@linux.vnet.ibm.com>

> ---
>   drivers/fsi/fsi-scom.c | 25 ++++++++++++++++++-------
>   1 file changed, 18 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/fsi/fsi-scom.c b/drivers/fsi/fsi-scom.c
> index c8eb5e5b94a7..3cba0eb645e1 100644
> --- a/drivers/fsi/fsi-scom.c
> +++ b/drivers/fsi/fsi-scom.c
> @@ -37,6 +37,7 @@ struct scom_device {
>   	struct list_head link;
>   	struct fsi_device *fsi_dev;
>   	struct miscdevice mdev;
> +	struct mutex lock;
>   	char	name[32];
>   	int idx;
>   };
> @@ -53,21 +54,26 @@ static int put_scom(struct scom_device *scom_dev, uint64_t value,
>   	int rc;
>   	uint32_t data;
>
> +	mutex_lock(&scom_dev->lock);
> +
>   	data = cpu_to_be32((value >> 32) & 0xffffffff);
>   	rc = fsi_device_write(scom_dev->fsi_dev, SCOM_DATA0_REG, &data,
>   				sizeof(uint32_t));
>   	if (rc)
> -		return rc;
> +		goto bail;
>
>   	data = cpu_to_be32(value & 0xffffffff);
>   	rc = fsi_device_write(scom_dev->fsi_dev, SCOM_DATA1_REG, &data,
>   				sizeof(uint32_t));
>   	if (rc)
> -		return rc;
> +		goto bail;
>
>   	data = cpu_to_be32(SCOM_WRITE_CMD | addr);
> -	return fsi_device_write(scom_dev->fsi_dev, SCOM_CMD_REG, &data,
> +	rc = fsi_device_write(scom_dev->fsi_dev, SCOM_CMD_REG, &data,
>   				sizeof(uint32_t));
> + bail:
> +	mutex_unlock(&scom_dev->lock);
> +	return rc;
>   }
>
>   static int get_scom(struct scom_device *scom_dev, uint64_t *value,
> @@ -76,27 +82,31 @@ static int get_scom(struct scom_device *scom_dev, uint64_t *value,
>   	uint32_t result, data;
>   	int rc;
>
> +
> +	mutex_lock(&scom_dev->lock);
>   	*value = 0ULL;
>   	data = cpu_to_be32(addr);
>   	rc = fsi_device_write(scom_dev->fsi_dev, SCOM_CMD_REG, &data,
>   				sizeof(uint32_t));
>   	if (rc)
> -		return rc;
> +		goto bail;
>
>   	rc = fsi_device_read(scom_dev->fsi_dev, SCOM_DATA0_REG, &result,
>   				sizeof(uint32_t));
>   	if (rc)
> -		return rc;
> +		goto bail;
>
>   	*value |= (uint64_t)cpu_to_be32(result) << 32;
>   	rc = fsi_device_read(scom_dev->fsi_dev, SCOM_DATA1_REG, &result,
>   				sizeof(uint32_t));
>   	if (rc)
> -		return rc;
> +		goto bail;
>
>   	*value |= cpu_to_be32(result);
>
> -	return 0;
> + bail:
> +	mutex_unlock(&scom_dev->lock);
> +	return rc;
>   }
>
>   static ssize_t scom_read(struct file *filep, char __user *buf, size_t len,
> @@ -183,6 +193,7 @@ static int scom_probe(struct device *dev)
>   	if (!scom)
>   		return -ENOMEM;
>
> +	mutex_init(&scom->lock);
>   	scom->idx = ida_simple_get(&scom_ida, 1, INT_MAX, GFP_KERNEL);
>   	snprintf(scom->name, sizeof(scom->name), "scom%d", scom->idx);
>   	scom->fsi_dev = fsi_dev;