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Date: Wed, 1 Jun 2022 17:31:13 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: <ira.weiny@...el.com>
CC: Dan Williams <dan.j.williams@...el.com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Alison Schofield <alison.schofield@...el.com>,
"Vishal Verma" <vishal.l.verma@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
"Ben Widawsky" <ben@...dawsk.net>, <linux-kernel@...r.kernel.org>,
<linux-cxl@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V9 6/9] cxl/port: Read CDAT table
On Wed, 1 Jun 2022 16:35:40 +0100
Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
> On Tue, 31 May 2022 08:26:29 -0700
> ira.weiny@...el.com wrote:
>
> > From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> >
> > The OS will need CDAT data from CXL devices to properly set up
> > interleave sets. Currently this is supported through a DOE mailbox
> > which supports CDAT.
> >
> > Cache the CDAT data for later parsing. Provide a sysfs binary attribute
> > to allow dumping of the CDAT.
> >
> > Binary dumping is modeled on /sys/firmware/ACPI/tables/
> >
> > The ability to dump this table will be very useful for emulation of real
> > devices once they become available as QEMU CXL type 3 device emulation will
> > be able to load this file in.
> >
> > This does not support table updates at runtime. It will always provide
> > whatever was there when first cached. Handling of table updates can be
> > implemented later.
> >
> > Finally create a complete list of DOE defines within cdat.h for code
> > wishing to decode the CDAT table.
> >
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > Co-developed-by: Ira Weiny <ira.weiny@...el.com>
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> >
>
> Fun question of ownership inline...
And a follow up due to triggering a bug that predated this series...
I'd send a fix, but I'm off on a long weekend shortly :)
>
> ...
>
> > +void read_cdat_data(struct cxl_port *port)
> > +{
> > + struct device *dev = &port->dev;
> > + size_t cdat_length;
> > + int ret;
> > +
> > + if (cxl_cdat_get_length(port, &cdat_length))
> > + return;
> > +
> > + port->cdat.table = devm_kzalloc(dev, cdat_length, GFP_KERNEL);
>
> boom. See below for why :)
>
> > + if (!port->cdat.table) {
> > + ret = -ENOMEM;
> > + goto error;
> > + }
> > +
> > + port->cdat.length = cdat_length;
> > + ret = cxl_cdat_read_table(port, &port->cdat);
> > + if (ret) {
> > + devm_kfree(dev, port->cdat.table);
> > + port->cdat.table = NULL;
> > + port->cdat.length = 0;
> > + ret = -EIO;
> > + goto error;
> > + }
> > +
> > + return;
> > +error:
> > + dev_err(dev, "CDAT data read error (%d)\n", ret);
> > +}
> > +EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);
> > diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> > index 2e2bd65c1024..aa4229ddc1bc 100644
> > --- a/drivers/cxl/core/port.c
> > +++ b/drivers/cxl/core/port.c
> > @@ -320,7 +320,48 @@ static void cxl_port_release(struct device *dev)
> > kfree(port);
> > }
> >
> > +static ssize_t cdat_read(struct file *filp, struct kobject *kobj,
> > + struct bin_attribute *bin_attr, char *buf,
> > + loff_t offset, size_t count)
> > +{
> > + struct device *dev = kobj_to_dev(kobj);
> > + struct cxl_port *port = to_cxl_port(dev);
> > +
> > + if (!port->cdat.table)
> > + return 0;
> > +
> > + return memory_read_from_buffer(buf, count, &offset,
> > + port->cdat.table,
> > + port->cdat.length);
> > +}
> > +
> > +static BIN_ATTR_RO(cdat, 0);
> > +
> > +static umode_t cxl_port_bin_attr_is_visible(struct kobject *kobj,
> > + struct bin_attribute *attr, int i)
> > +{
> > + struct device *dev = kobj_to_dev(kobj);
> > + struct cxl_port *port = to_cxl_port(dev);
> > +
> > + if ((attr == &bin_attr_cdat) && port->cdat.table)
> > + return 0400;
> > +
> > + return 0;
> > +}
> > +
> > +static struct bin_attribute *cxl_cdat_bin_attributes[] = {
> > + &bin_attr_cdat,
> > + NULL,
> > +};
> > +
> > +static struct attribute_group cxl_cdat_attribute_group = {
> > + .name = "CDAT",
> > + .bin_attrs = cxl_cdat_bin_attributes,
> > + .is_bin_visible = cxl_port_bin_attr_is_visible,
> > +};
> > +
> > static const struct attribute_group *cxl_port_attribute_groups[] = {
> > + &cxl_cdat_attribute_group,o
> > &cxl_base_attribute_group,
> > NULL,
> > };
> > @@ -462,6 +503,8 @@ struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> > return port;
> >
> > cxl_find_cdat_mb(port);
> > + /* Cache the data early to ensure is_visible() works */
> > + read_cdat_data(port);
>
> This uses port as the 'device' for devm_ calls.
> Unfortunately if the port driver isn't loaded, it still "successfully" runs.
> Then if the port driver is probed, you get both a bunch of errors due to
> devm_ allocations on a device before the driver is loaded.
>
> For extra fun it tries to probe the ports multiple times without freeing
> the index which is 'interesting'. We had this happen a while ago (unrelated
> to DOE) but this may be unrelated (or maybe related to the region stuff
> I'm carrying on my test tree)
So the extra devices are a result of the obvious initial path of
cxl_mem_probe() from module probe and down failing, then bus_rescan_devices
coming along from the pmem driver having another go...
So next question is why don't the first set of endpointX devices get cleaned up
if the create_endpoint() in cxl/mem.c fails.
I think this is because the cxl_endpoint_autoremove() call hasn't yet happened
when we detect the failure to bind a driver and error out of cxl_mem_probe().
So, fix is probably to do the cxl_endpoint_autoremove() unconditionally
by moving it before the check on driver binding.
https://elixir.bootlin.com/linux/latest/source/drivers/cxl/mem.c#L67
Move it up a few lines.
>
> As to the question of what the correct fix is...
> Maybe move them into the port driver probe but then is_visible
> won't work. Or pass a pointer to the struct device *host down
> into read_cdat_data and __read_cdat_data calls to handle the
> allocation. (I tried this and it seems superficially fine).
>
> Jonathan
>
>
>
> >
> > dev = &port->dev;
> > if (is_cxl_memdev(uport))
> > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> > index 0a86be589ffc..531b77d296c7 100644
> > --- a/drivers/cxl/cxl.h
> > +++ b/drivers/cxl/cxl.h
> > @@ -8,6 +8,7 @@
> > #include <linux/bitfield.h>
> > #include <linux/bitops.h>
> > #include <linux/io.h>
> > +#include "cdat.h"
> >
> > /**
> > * DOC: cxl objects
> > @@ -268,6 +269,7 @@ struct cxl_nvdimm {
> > * @dead: last ep has been removed, force port re-creation
> > * @depth: How deep this port is relative to the root. depth 0 is the root.
> > * @cdat_mb: Mailbox which supports the CDAT protocol
> > + * @cdat: Cached CDAT data
> > */
> > struct cxl_port {
> > struct device dev;
> > @@ -280,6 +282,7 @@ struct cxl_port {
> > bool dead;
> > unsigned int depth;
> > struct pci_doe_mb *cdat_mb;
> > + struct cxl_cdat cdat;
> > };
> >
> > /**
> > diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
> > index 366b21bd1a01..35f0d4892eaa 100644
> > --- a/drivers/cxl/cxlpci.h
> > +++ b/drivers/cxl/cxlpci.h
> > @@ -75,4 +75,5 @@ int devm_cxl_port_enumerate_dports(struct cxl_port *port);
> > struct cxl_dev_state;
> > int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm);
> > void cxl_find_cdat_mb(struct cxl_port *port);
> > +void read_cdat_data(struct cxl_port *port);
> > #endif /* __CXL_PCI_H__ */
>
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