Re: [PATCH v2 4/9] powerpc/pseries: Send payload with ibm,send-hvpipe-msg RTAS

[Haren Myneni <haren@linux.ibm.com>]

On Mon, 2025-08-25 at 11:28 +0530, Mahesh J Salgaonkar wrote:
> On 2025-08-12 15:57:08 Tue, Haren Myneni wrote:
> > ibm,send-hvpipe-msg RTAS call is used to send data to the source
> > (Ex: Hardware Management Console) over the hypervisor pipe. The
> > maximum data length of 4048 bytes is supported with this RTAS call
> > right now. The user space uses write() to send this payload which
> > invokes this RTAS. Then the write returns the buffer length
> > (including papr_hvpipe_hdr length) to the user space for success
> > or RTAS failure error.
> > 
> > ibm,send-hvpipe-msg call takes source ID as target and the buffer
> > in the form of buffer list. The buffer list format consists of
> > work area of size 4K to hold buffer list and number of 4K work
> > areas depends on buffers is as follows:
> > 
> > Length of Buffer List in bytes
> > Address of 4K buffer 1
> > Length of 4K buffer 1 used
> > ...
> > Address of 4K buffer n
> > Length of 4K buffer n used
> > 
> > Only one buffer is used right now because of max payload size is
> > 4088 bytes. writev() can be used in future when supported more
> 
> Do you mean 4048 ?
Yes typo error. It should be 4048 bytes as mentioned in the code.

> 
> > than one buffer.
> > 
> > Signed-off-by: Haren Myneni <haren@linux.ibm.com>
> > ---
> >  arch/powerpc/platforms/pseries/papr-hvpipe.c | 120
> > ++++++++++++++++++-
> >  arch/powerpc/platforms/pseries/papr-hvpipe.h |   7 ++
> >  2 files changed, 126 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/platforms/pseries/papr-hvpipe.c
> > b/arch/powerpc/platforms/pseries/papr-hvpipe.c
> > index 5768d072859d..c30f4d75e645 100644
> > --- a/arch/powerpc/platforms/pseries/papr-hvpipe.c
> > +++ b/arch/powerpc/platforms/pseries/papr-hvpipe.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/of.h>
> >  #include <asm/machdep.h>
> >  #include <asm/rtas.h>
> > +#include <asm/rtas-work-area.h>
> >  #include <uapi/asm/papr-hvpipe.h>
> >  #include "pseries.h"
> >  #include "papr-hvpipe.h"
> > @@ -59,6 +60,51 @@ static LIST_HEAD(hvpipe_src_list);
> >   *   return code for failure.
> >   */
> >  
> > +/*
> > + * ibm,send-hvpipe-msg RTAS call
> > + * @area: Caller-provided work area buffer to send.
> > + * @srcID: Target source for the send pipe message.
> > + */
> > +static int rtas_ibm_send_hvpipe_msg(struct rtas_work_area *area,
> > u32 srcID)
> > +{
> > +	const s32 token =
> > rtas_function_token(RTAS_FN_IBM_SEND_HVPIPE_MSG);
> > +	s32 fwrc;
> > +	int ret;
> > +
> > +	if (token == RTAS_UNKNOWN_SERVICE)
> > +		return -ENOENT;
> > +
> > +	do {
> > +		fwrc = rtas_call(token, 2, 1, NULL, srcID,
> > +				rtas_work_area_phys(area));
> > +
> > +	} while (rtas_busy_delay(fwrc));
> > +
> > +	switch (fwrc) {
> > +	case RTAS_SUCCESS:
> > +		ret = 0;
> > +		break;
> > +	case RTAS_HARDWARE_ERROR:
> > +		ret = -EIO;
> > +		break;
> > +	case RTAS_INVALID_PARAMETER:
> > +		ret = -EINVAL;
> > +		break;
> > +	case RTAS_HVPIPE_CLOSED:
> > +		ret = -EACCES;
> 
> The status -4 is Pipe connection is closed/unavailabe. Instead of
> permission denied does it make sense to return -EPIPE (Broken pipe) ?

Agree, The user space should close all FDs when sees this error. Will
change it to -EPIPE.

Thanks for your suggestions.

> 
> > +		break;
> > +	case RTAS_FUNC_NOT_SUPPORTED:
> > +		ret = -EOPNOTSUPP;
> > +		break;
> > +	default:
> > +		ret = -EIO;
> > +		pr_err_ratelimited("unexpected ibm,receive-hvpipe-msg
> > status %d\n", fwrc);
> > +		break;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> [...]
> 
> Thanks,
> -Mahesh.