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

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Message-ID: <33924c2e545b2dfabf2849d9c485f165c339323f.camel@kernel.crashing.org>
Date:   Mon, 18 Jun 2018 14:46:33 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Alistair Popple <alistair@...ple.id.au>, openbmc@...ts.ozlabs.org
Cc:     Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...id.au>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 5/5] fsi/scom: Major overhaul

On Mon, 2018-06-18 at 14:09 +1000, Alistair Popple wrote:
> On Sunday, 17 June 2018 11:22:11 AM AEST Benjamin Herrenschmidt wrote:
> > On Sun, 2018-06-17 at 11:17 +1000, Benjamin Herrenschmidt wrote:
> > > 
> > > We have everything that cronus needs and more than pdbg needs afaik :-)
> 
> Yep, has what we need and more (such as put scom under mask and indirect scom).
> Only other useful thing would be repeated getsom/putscom operations (eg. read
> the same scom address n times) as they would help with ADU access which can do
> autoincrement or scanscom (although we should just use the scan engine directly
> for that so not a big issue).
> 
> > +	for (retries = 0; retries < SCOM_MAX_RETRIES; retries++) {
> > +		rc = raw_get_scom(scom, value, addr, &status);
> > +		if (rc) {
> > +			/* Try resetting the bridge if FSI fails */
> > +			if (rc != -ENODEV && retries == 0) {
> > +				fsi_device_write(scom->fsi_dev, SCOM_FSI2PIB_RESET_REG,
> > +						 &dummy, sizeof(uint32_t));
> > +				rc = -EBUSY;
> > +			} else
> > +				return rc;
> > +		} else
> > +			rc = handle_fsi2pib_status(scom, status);
> > +		if (rc && rc != -EBUSY)
> > +			break;
> > +		if (rc == 0) {
> > +			rc = handle_pib_status(scom,
> > +					       (status & SCOM_STATUS_PIB_RESP_MASK)
> > +					       >> SCOM_STATUS_PIB_RESP_SHIFT);
> > +			if (rc && rc != -EBUSY)
> > +				break;
> > +		}
> > +		if (rc == 0)
> > +			break;
> > +		msleep(1);
> > +	}
> 
> The rc handling above took me a little while to grok but I didn't come up with a
> cleaner alternative and I think it's correct.

Ack-by or Reviewed-by tag pls ? :-)

Cheers,
Ben.

> - Alistair
> 
> > > 
> > > That said, cronus does a bunch of other stupid things that I'm still
> > > trying to figure out how to fix.
> > > 
> > > We might need to create a /dev/cfam rather than going through that
> > > magic sysfs "raw" file, and I wouldn't mind using a single IDA so that
> > > all the devices below a given FSI slace (cfam itself, sbefifo, occ,
> > > ...) have the same "number".
> > 
> > Also while we're at reworking how all this is exposed to our broken
> > userspace, I wouldn't mind putting all these dev entries under a
> > directory, if I can figure out how to do that (I haven't really looked
> > yet).
> > 
> > /dev/fsi/{cfamN,sbefifoN,occN, ...} and possibly similar by-id and by-
> > path that other subsystems use, so we have something more deterministic
> > than the "random number" crap we do now.
> > 
> > We can always keep hacks to do symlinks in our kernel tree until we
> > have converted all our userspace users.
> > 
> > We currently control the only userspace users of this, so now is a good
> > time to cleanup how we expose things. This won't always be the case.
> > 
> > Cheers,
> > Ben.
> > 
> > 
> 
>