Re: [RFC PATCH 5/5] fsi/scom: Major overhaul

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2018-06-13 at 09:57 -0500, Eddie James wrote:
> 
> On 06/12/2018 12:19 AM, Benjamin Herrenschmidt wrote:
> > This was too hard to split ... this adds a number of features
> > to the SCOM user interface:
> > 
> >   - Support for indirect SCOMs
> > 
> >   - read()/write() interface now handle errors and retries
> > 
> >   - New ioctl() "raw" interface for use by debuggers
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> >   drivers/fsi/fsi-scom.c   | 424 ++++++++++++++++++++++++++++++++++++---
> >   include/uapi/linux/fsi.h |  56 ++++++
> >   2 files changed, 450 insertions(+), 30 deletions(-)
> >   create mode 100644 include/uapi/linux/fsi.h
> > 
> > diff --git a/drivers/fsi/fsi-scom.c b/drivers/fsi/fsi-scom.c
> > index e98573ecdae1..39c74351f1bf 100644
> > --- a/drivers/fsi/fsi-scom.c
> > +++ b/drivers/fsi/fsi-scom.c
> > @@ -24,6 +24,8 @@
> >   #include <linux/list.h>
> >   #include <linux/idr.h>
> > +
> > +static int scom_reset(struct scom_device *scom, void __user *argp)
> > +{
> > +	uint32_t flags, dummy = -1;
> > +	int rc = 0;
> > +
> > +	if (get_user(flags, (__u32 __user *)argp))
> > +		return -EFAULT;
> > +	if (flags & SCOM_RESET_PIB)
> > +		rc = fsi_device_write(scom->fsi_dev, SCOM_PIB_RESET_REG, &dummy,
> > +				      sizeof(uint32_t));
> 
> I realize this is a user requested flag but I believe the BMC is never 
> supposed to issue this type of reset, due to the possibility of breaking 
> stuff on the host side. Not sure if it should even be available?

It's for use by cronus or similar low level system debuggers.

Cheers,
Ben.

> Otherwise, looks good!
> Thanks,
> Eddie
> 
> > +	if (!rc && (flags & (SCOM_RESET_PIB | SCOM_RESET_INTF)))
> > +		rc = fsi_device_write(scom->fsi_dev, SCOM_FSI2PIB_RESET_REG, &dummy,
> > +				      sizeof(uint32_t));
> > +	return rc;
> > +}
> > +
> > +static int scom_check(struct scom_device *scom, void __user *argp)
> > +{
> > +	/* Still need to find out how to get "protected" */
> > +	return put_user(SCOM_CHECK_SUPPORTED, (__u32 __user *)argp);
> > +}
> > +
> > +static long scom_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > +{
> > +	struct miscdevice *mdev = file->private_data;
> > +	struct scom_device *scom = to_scom_dev(mdev);
> > +	void __user *argp = (void __user *)arg;
> > +	int rc = -ENOTTY;
> > +
> > +	mutex_lock(&scom->lock);
> > +	switch(cmd) {
> > +	case FSI_SCOM_CHECK:
> > +		rc = scom_check(scom, argp);
> > +		break;
> > +	case FSI_SCOM_READ:
> > +		rc = scom_raw_read(scom, argp);
> > +		break;
> > +	case FSI_SCOM_WRITE:
> > +		rc = scom_raw_write(scom, argp);
> > +		break;
> > +	case FSI_SCOM_RESET:
> > +		rc = scom_reset(scom, argp);
> > +		break;
> > +	}
> > +	mutex_unlock(&scom->lock);
> > +	return rc;
> > +}
> > +
> >   static const struct file_operations scom_fops = {
> > -	.owner	= THIS_MODULE,
> > -	.llseek	= scom_llseek,
> > -	.read	= scom_read,
> > -	.write	= scom_write,
> > +	.owner		= THIS_MODULE,
> > +	.llseek		= scom_llseek,
> > +	.read		= scom_read,
> > +	.write		= scom_write,
> > +	.unlocked_ioctl	= scom_ioctl,
> >   };
> > 
> >   static int scom_probe(struct device *dev)
> > diff --git a/include/uapi/linux/fsi.h b/include/uapi/linux/fsi.h
> > new file mode 100644
> > index 000000000000..6008d93f2e48
> > --- /dev/null
> > +++ b/include/uapi/linux/fsi.h
> > @@ -0,0 +1,56 @@
> > +#ifndef _UAPI_LINUX_FSI_H
> > +#define _UAPI_LINUX_FSI_H
> > +
> > +#include <linux/ioctl.h>
> > +
> > +/*
> > + * /dev/scom "raw" ioctl interface
> > + *
> > + * The driver supports a high level "read/write" interface which
> > + * handles retries and converts the status to Linux error codes,
> > + * however low level tools an debugger need to access the "raw"
> > + * HW status information and interpret it themselves, so this
> > + * ioctl interface is also provided for their use case.
> > + */
> > +
> > +/* Structure for SCOM read/write */
> > +struct scom_access {
> > +	__u64	addr;		/* SCOM address, supports indirect */
> > +	__u64	data;		/* SCOM data (in for write, out for read) */
> > +	__u64	mask;		/* Data mask for writes */
> > +	__u32	intf_errors;	/* Interface error flags */
> > +#define SCOM_INTF_ERR_PARITY		0x00000001 /* Parity error */
> > +#define SCOM_INTF_ERR_PROTECTION	0x00000002 /* Blocked by secure boot */
> > +#define SCOM_INTF_ERR_ABORT		0x00000004 /* PIB reset during access */
> > +#define SCOM_INTF_ERR_UNKNOWN		0x80000000 /* Unknown error */
> > +	/*
> > +	 * Note: Any other bit set in intf_errors need to be considered as an
> > +	 * error. Future implementations may define new error conditions. The
> > +	 * pib_status below is only valid if intf_errors is 0.
> > +	 */
> > +	__u8	pib_status;	/* 3-bit PIB status */
> > +#define SCOM_PIB_SUCCESS	0	/* Access successful */
> > +#define SCOM_PIB_BLOCKED	1	/* PIB blocked, pls retry */
> > +#define SCOM_PIB_OFFLINE	2	/* Chiplet offline */
> > +#define SCOM_PIB_PARTIAL	3	/* Partial good */
> > +#define SCOM_PIB_BAD_ADDR	4	/* Invalid address */
> > +#define SCOM_PIB_CLK_ERR	5	/* Clock error */
> > +#define SCOM_PIB_PARITY_ERR	6	/* Parity error on the PIB bus */
> > +#define SCOM_PIB_TIMEOUT	7	/* Bus timeout */
> > +	__u8	pad;
> > +};
> > +
> > +/* Flags for SCOM check */
> > +#define SCOM_CHECK_SUPPORTED	0x00000001	/* Interface supported */
> > +#define SCOM_CHECK_PROTECTED	0x00000002	/* Interface blocked by secure boot */
> > +
> > +/* Flags for SCOM reset */
> > +#define SCOM_RESET_INTF		0x00000001	/* Reset interface */
> > +#define SCOM_RESET_PIB		0x00000002	/* Reset PIB */
> > +
> > +#define FSI_SCOM_CHECK	_IOR('s', 0x00, __u32)
> > +#define FSI_SCOM_READ	_IOWR('s', 0x01, struct scom_access)
> > +#define FSI_SCOM_WRITE	_IOWR('s', 0x02, struct scom_access)
> > +#define FSI_SCOM_RESET	_IOW('s', 0x03, __u32)
> > +
> > +#endif /* _UAPI_LINUX_FSI_H */