Re: [PATCH 3/3] platform/x86: Intel PMT Telemetry capability driver
From: Andy Shevchenko
Date: Tue May 05 2020 - 09:50:00 EST
On Tue, May 5, 2020 at 5:32 AM David E. Box <david.e.box@xxxxxxxxxxxxxxx> wrote:
...
> Register mappings are not provided by the driver. Instead, a GUID is read
> from a header for each endpoint. The GUID identifies the device and is to
> be used with an XML, provided by the vendor, to discover the available set
> of metrics and their register mapping. This allows firmware updates to
> modify the register space without needing to update the driver every time
> with new mappings. Firmware writes a new GUID in this case to specify the
> new mapping. Software tools with access to the associated XML file can
> then interpret the changes.
Is old hardware going to support this in the future?
(I have in mind Apollo Lake / Broxton)
> This module manages access to all PMT Telemetry endpoints on a system,
> regardless of the device exporting them. It creates an intel_pmt_telem
Name is not the best we can come up with. Would anyone else use PMT?
Would it be vendor-agnostic ABI?
(For example, I know that MIPI standardizes tracing protocols, like
STM, do we have any plans to standardize this one?)
telem -> telemetry.
> class to manage the list. For each endpoint, sysfs files provide GUID and
> size information as well as a pointer to the parent device the telemetry
> comes from. Software may discover the association between endpoints and
> devices by iterating through the list in sysfs, or by looking for the
> existence of the class folder under the device of interest. A device node
> of the same name allows software to then map the telemetry space for direct
> access.
...
> + tristate "Intel PMT telemetry driver"
I think user should understand what is it from the title (hint: spell
PMT fully).
...
> obj-$(CONFIG_PMC_ATOM) += pmc_atom.o
> +obj-$(CONFIG_INTEL_PMT_TELEM) += intel_pmt_telem.o
Keep this and Kconfig section in order with the other stuff.
...
bits.h?
> +#include <linux/cdev.h>
> +#include <linux/intel-dvsec.h>
> +#include <linux/io-64-nonatomic-lo-hi.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pci.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/xarray.h>
...
> +/* platform device name to bind to driver */
> +#define TELEM_DRV_NAME "pmt_telemetry"
Shouldn't be part of MFD header?
...
> +#define TELEM_TBIR_MASK 0x7
GENMASK() ?
> +struct pmt_telem_priv {
> + struct device *dev;
> + struct intel_dvsec_header *dvsec;
> + struct telem_header header;
> + unsigned long base_addr;
> + void __iomem *disc_table;
> + struct cdev cdev;
> + dev_t devt;
> + int devid;
> +};
...
> + unsigned long phys = priv->base_addr;
> + unsigned long pfn = PFN_DOWN(phys);
> + unsigned long psize;
> +
> + psize = (PFN_UP(priv->base_addr + priv->header.size) - pfn) * PAGE_SIZE;
> + if (vsize > psize) {
> + dev_err(priv->dev, "Requested mmap size is too large\n");
> + return -EINVAL;
> + }
...
> +static ssize_t guid_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + struct pmt_telem_priv *priv = dev_get_drvdata(dev);
> +
> + return sprintf(buf, "0x%x\n", priv->header.guid);
> +}
So, it's not a GUID but rather some custom number? Can we actually do
a real GUID / UUID here?
Because of TODO below I suppose it's not carved in stone (yet) and
basically a protocol defined by firmware (which can be amended).
...
> + /* TODO: replace with device properties??? */
So, please, fulfill. swnode I guess is what you are looking for.
> + priv->dvsec = dev_get_platdata(&pdev->dev);
> + if (!priv->dvsec) {
> + dev_err(&pdev->dev, "Platform data not found\n");
> + return -ENODEV;
> + }
...
> + /* Local access and BARID only for now */
> + switch (priv->header.access_type) {
> + case TELEM_ACCESS_LOCAL:
> + if (priv->header.tbir) {
> + dev_err(&pdev->dev,
> + "Unsupported BAR index %d for access type %d\n",
> + priv->header.tbir, priv->header.access_type);
> + return -EINVAL;
> + }
> + fallthrough;
What's the point?
> +
> + case TELEM_ACCESS_BARID:
> + break;
> + default:
> + dev_err(&pdev->dev, "Unsupported access type %d\n",
> + priv->header.access_type);
> + return -EINVAL;
> + }
> + err = alloc_chrdev_region(&priv->devt, 0, 1, TELEM_DRV_NAME);
err or ret? Be consistent in the module.
> + if (err < 0) {
' < 0' Do we need it?
> + dev_err(&pdev->dev,
> + "PMT telemetry chrdev_region err: %d\n", err);
> + return err;
> + }
...
> + err = pmt_telem_create_dev(priv);
> + if (err < 0)
' < 0' Do we need it?
> + goto fail_create_dev;
> +
> + return 0;
> +}
...
> +static const struct platform_device_id pmt_telem_table[] = {
> + {
> + .name = "pmt_telemetry",
> + }, {
> + /* sentinel */
> + }
{ .name = ... },
{}
is enough.
> +};
...
> +static int __init pmt_telem_init(void)
> +{
> + int ret = class_register(&pmt_telem_class);
> +
> + if (ret)
int ret;
ret = ...
if (ret)
> + return ret;
> +
> + ret = platform_driver_register(&pmt_telem_driver);
> + if (ret)
> + class_unregister(&pmt_telem_class);
> +
> + return ret;
> +}
...
> +{
> +}
> +
Extra blank line.
> +module_init(pmt_telem_init);
> +module_exit(pmt_telem_exit);
Better to attach to the respective functions.
...
> +#include <linux/intel-dvsec.h>
There is no user of this below, but types.h has users here.
> +/* Telemetry types */
> +#define PMT_TELEM_TELEMETRY 0
> +#define PMT_TELEM_CRASHLOG 1
> +
> +struct telem_header {
> + u8 access_type;
If it's part of hardware communication, shouldn't be rather __uXX
types to show that this is part of protocol between software and
hardware?
> + u8 telem_type;
> + u16 size;
> + u32 guid;
> + u32 base_offset;
> + u8 tbir;
> +};
--
With Best Regards,
Andy Shevchenko