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

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Message-ID: <2586161.J3ITyiHLyu@new-mexico>
Date:   Mon, 18 Jun 2018 15:05:46 +1000
From:   Alistair Popple <alistair@...ple.id.au>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     openbmc@...ts.ozlabs.org, 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 Monday, 18 June 2018 2:46:33 PM AEST Benjamin Herrenschmidt wrote:
> 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 ? :-)

Oh, sure:

Reviewed-by: Alistair Popple <alistair@...ple.id.au>

> 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.
> > > 
> > > 
> > 
> > 
>