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Date:	Mon, 16 May 2016 15:45:50 +0530
From:	Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	platform-driver-x86@...r.kernel.org,
	"dvhart@...radead.org" <dvhart@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olof@...om.net>, vishwanath.somayaji@...el.com
Subject: Re: [PATCH v4] platform:x86: Add PMC Driver for Intel Core SOC

On Thu, May 12, 2016 at 06:02:45PM +0300, Andy Shevchenko wrote:
> On Thu, May 12, 2016 at 4:50 PM, Rajneesh Bhardwaj
> <rajneesh.bhardwaj@...el.com> wrote:
> 
> Sorry for a bit late review, but I think there are still issues need
> to be addressed.
>

Thanks for the detailed review and the feedback. :)
 
> > This patch adds the Power Management Controller driver as a pci driver
> > for Intel Core SOC architecture.
> 
> SOC -> SoC
> 

Sure, will fix this throughout the code.

> >
> > This driver can utilize debugging capabilities and supported features
> > as exposed by the Power Management Controller.
> >
> > Please refer to the below specification for more details on PMC features.
> > http://www.intel.in/content/www/in/en/chipsets/100-series-chipset-datasheet-vol-2.html
> >
> > The current version of this driver exposes slp_s0_residency counter.
> > This counter can be used for detecting fragile SLP_S0 signal related
> > failures and take corrective actions when PCH SLP_S0 signal is not
> > asserted after kernel freeze as part of suspend to idle flow
> > (echo freeze > /sys/power/state).
> >
> > Intel Platform Controller Hub (PCH) asserts SLP_S0 signal when it
> > detects favorable conditions to enter its low power mode. As a
> > pre-requisite the SOC should be in deepest possible Package C-State
> > and devices should be in low power mode. For example, on Skylake SOC
> 
> Ditto.
> Check entire code for this.
> 

Same as above.

> > the deepest Package C-State is Package C10 or PC10. Suspend to idle
> > flow generally leads to PC10 state but PC10 state may not be sufficient
> > for realizing the platform wide power potential which SLP_S0 signal
> > assertion can provide.
> >
> > SLP_S0 signal is often connected to the Embedded Controller (EC) and the
> > Power Management IC (PMIC) for other platform power management related
> > optimizations.
> >
> > In general, SLP_S0 assertion == PC10 + PCH low power mode + ModPhy Lanes
> > power gated + PLL Idle.
> >
> > As part of this driver, a mechanism to read the slp_s0 residency is exposed
> > as an api and also debugfs features are added to indicate slp_s0 signal
> 
> api -> API
> 

Sure, will take care of this change.

> > assertion residency in microseconds.
> >
> > echo freeze > /sys/power/state
> > wake the system
> > cat /sys/kernel/debug/pmc_core/slp_s0_residency_usec
> >
> > Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>
> > Signed-off-by: Vishwanath Somayaji <vishwanath.somayaji@...el.com>
> 
> Two people (1).
> 
> 

Ok.

> > +INTEL PMC CORE DRIVER
> > +M:      Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>
> > +M:      Vishwanath Somayaji <vishwanath.somayaji@...el.com>
> > +L:      platform-driver-x86@...r.kernel.org
> > +S:      Maintained
> > +F:      drivers/platform/x86/intel_pmc_core.h
> > +F:      drivers/platform/x86/intel_pmc_core.c
> 
> So, we have arch/x86/platform/atom/pmc_atom.c
> 
> This driver looks very similar (by what functional is), so, we have to
> become clear what our layout is.
> Either we go with drivers/platform/x86 or with arch/x86/platform.
> 

IMHO, the functianality provided by this driver is platform specific and
not architecture specific.

There are few similar drivers present in this location already i.e.
intel_telemetry_core.c, intel_pmc_ipc.c etc.

We had initially put this driver along with pmc_atom.c but later we thought
that driver/platform/x86 would be a more apt place for it because of the
above mentioned reasons.

Please advise for the right location for this driver if its not placed in the
expected location.

> > --- a/drivers/platform/x86/Kconfig
> > +++ b/drivers/platform/x86/Kconfig
> > @@ -821,6 +821,18 @@ config INTEL_IPS
> >           functionality.  If in doubt, say Y here; it will only load on
> >           supported platforms.
> >
> > +config INTEL_PMC_CORE
> 
> Better to locate this in alphabetical order.
> 

Agreed, i tried to put it in alphabetical order but there are quite a few entries
in Kconfig that are skewed e.g. INTEL_MFLD is placed above INTEL_IPS.

Placing INTEL_PMC_CORE after INTEL_IMR would be ok?

> > +       bool "Intel PMC Core driver"
> > +       depends on X86 && PCI
> 
> > +       ---help---
> > +         The Intel Platform Controller Hub for Intel Core SoCs provides access
> > +         to Power Management Controller registers via a pci interface. This
> > +         driver can utilize debugging capabilities and supported features as
> > +         exposed by the Power Management Controller.
> > +
> > +         Supported features:
> > +               - slp_s0_residency counter.
> > +
> >  config INTEL_IMR
> >         bool "Intel Isolated Memory Region support"
> >         default n
> > diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
> > index 448443c..9b11b40 100644
> > --- a/drivers/platform/x86/Makefile
> > +++ b/drivers/platform/x86/Makefile
> > @@ -69,3 +69,4 @@ obj-$(CONFIG_INTEL_PUNIT_IPC)  += intel_punit_ipc.o
> >  obj-$(CONFIG_INTEL_TELEMETRY)  += intel_telemetry_core.o \
> >                                    intel_telemetry_pltdrv.o \
> >                                    intel_telemetry_debugfs.o
> > +obj-$(CONFIG_INTEL_PMC_CORE)    += intel_pmc_core.o
> > diff --git a/drivers/platform/x86/intel_pmc_core.c b/drivers/platform/x86/intel_pmc_core.c
> > new file mode 100644
> > index 0000000..0b5388e
> > --- /dev/null
> > +++ b/drivers/platform/x86/intel_pmc_core.c
> > @@ -0,0 +1,201 @@
> > +/*
> > + * Intel Core SOC Power Management Controller Driver
> > + *
> > + * Copyright (c) 2016, Intel Corporation.
> > + * All Rights Reserved.
> 
> > + * Author: Rajneesh Bhardwaj (rajneesh.bhardwaj@...el.com)
> 
> (2)
> 
> In (1) you put two people, here is one. Please, explain who is the
> author and why SoB is not in align with Author(s).
> 

Its a miss from our end, will update the Author tag. Thanks for pointing it out.

> > + *
> > + * This program is free software; you can redistribute it and/or modify it
> > + * under the terms and conditions of the GNU General Public License,
> > + * version 2, as published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope it will be useful, but WITHOUT
> > + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> > + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> > + * more details.
> > + *
> > + */
> > +
> > +#include <linux/init.h>
> > +#include <linux/pci.h>
> > +#include <linux/device.h>
> > +#include <linux/debugfs.h>
> > +#include <linux/seq_file.h>
> > +#include <linux/module.h>
> > +#include <linux/io.h>
> 
> Alphabetical order.
> 
> + empty line
> 
> > +#include <asm/cpu_device_id.h>
> 
> + empty line
> 
> > +#include "intel_pmc_core.h"
> > +
> 

Ok for above.

> > +static struct pmc_dev pmc;
> > +
> > +static const struct pci_device_id pmc_pci_ids[] = {
> > +       { PCI_VDEVICE(INTEL, SPT_PMC_PCI_DEVICE_ID), (kernel_ulong_t)NULL },
> 
> No need to have an explicit NULL
> 

There is a precedent in the kernel for such usage and in previous reviews we agreed
to stick to this format. I hope thats fine?

> > +       { 0, },
> > +};
> > +MODULE_DEVICE_TABLE(pci, pmc_pci_ids);
> > +
> > +/**
> > + * intel_pmc_slp_s0_counter_read() - Read slp_s0 residency.
> > + * @data: Out param that contains current slp_s0 count.
> > + *
> > + * This API currently supports Intel Skylake SOC and Sunrise
> > + * point Platform Controller Hub. Future platform support
> 
> Either Sunrisepoint or Sunrise Point.
> SOC -> SoC
> 

Sure.

> > + * should be added for platforms that support low power modes
> > + * beyond Package C10 state.
> > + *
> > + * SLP_S0_RESIDENCY counter counts in 100 us granularity per
> > + * step hence function populates the multiplied value in out
> > + * parameter @data
> 
> + dot at the end of sentence.
> 

Ok.

> > + *
> > + * Return:     an error code or 0 on success.
> > + */
> > +int intel_pmc_slp_s0_counter_read(u64 *data)
> > +{
> 
> struct pmc_dev *pmcdev = &pmc;
> 
> 
> > +       if (!pmc.has_slp_s0_res)
> 
> 'pmc.' -> 'pmcdev->'
> 
> > +               return -EACCES;
> > +
> > +       *data = readl(pmc.regmap + SPT_PMC_SLP_S0_RES_COUNTER_OFFSET);
> 
> Ditto.
> 
> > +       *data *= SPT_PMC_SLP_S0_RES_COUNTER_STEP;
> 
> Use temporary variable.
> 
> u64 value;
> 
> value = readl();
> value *= ;
> 
> *data = value;
> 
> This makes only one place where you assign returning value.
>

Ok, will rework on the function and split it into two. One for performing
read operation and callable from within the module and the other one to be
called from outside.
 
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(intel_pmc_slp_s0_counter_read);
> 
> Who is going to be a user of that?
> 

This is expected to be used by a framework (upcoming) for detecting slp_s0
signal assertion related failures.

> > +
> 
> > +#if IS_ENABLED(CONFIG_DEBUG_FS)
> 
> 
> > +static int pmc_core_dev_state_show(struct seq_file *s, void *unused)
> > +{
> 
> Pointer to pmc, i.e. pmc_dev *, would be supplied in seq_file. Take it
> from there...
> 
> > +       u64 counter_val;
> 
> u64 value;
> 
> > +       int err;
> > +
> > +       err = intel_pmc_slp_s0_counter_read(&counter_val);
> 
> ...thus split your function to internal, which takes pmc_dev * as a
> first parameter and use exported variant for users which takes global
> variable.
> 
> int intel_pmc_slp_s0_counter_read(u64 *data)
> {
>  struct pmc_dev *pmcdev = &pmc;
> 
>  return do_counter_read(pmcdev, data);
> }
> 
> 

As explained above, will rework on the function split logic and accomodate 
these suggestions.

> > +       if (!err)
> > +               seq_printf(s, "%lld\n", counter_val);
> 
> Please, use positive check
> 
> if (err)
>  return err;
> 

Ok, any benefit? readability?

> > +
> > +       return err;
> > +}
> > +
> > +static int pmc_core_dev_state_open(struct inode *inode, struct file *file)
> > +{
> > +       return single_open(file, pmc_core_dev_state_show, inode->i_private);
> > +}
> > +
> > +static const struct file_operations pmc_core_dev_state_ops = {
> > +       .open           = pmc_core_dev_state_open,
> > +       .read           = seq_read,
> > +       .llseek         = seq_lseek,
> > +       .release        = single_release,
> > +};
> > +
> 
> > +static void pmc_core_dbgfs_unregister(struct pmc_dev *pmc)
> > +{
> > +       debugfs_remove_recursive(pmc->dbgfs_dir);
> > +}
> 
> No need to keep this under #ifdef.
> 

Based on some previus review comments we decided to put the dummy functions
for !CONIG_DEBUG_FS case. Can you please elaborate more on this change request?

> > +
> > +static int pmc_core_dbgfs_register(struct pmc_dev *pmc)
> > +{
> > +       struct dentry *dir, *file;
> 
> > +       int ret = 0;
> 
> Redundant, see below.
> 
> > +
> > +       dir = debugfs_create_dir("pmc_core", NULL);
> > +       if (!dir)
> > +               return -ENOMEM;
> > +
> > +       pmc->dbgfs_dir = dir;
> > +       file = debugfs_create_file("slp_s0_residency_usec", S_IFREG | S_IRUGO,
> > +                                  dir, pmc, &pmc_core_dev_state_ops);
> > +
> > +       if (!file) {
> > +               pmc_core_dbgfs_unregister(pmc);
> > +               ret = -ENODEV;
> 
> return -ENODEV;
> 

Ok.

> > +       }
> 
> > +       return ret;
> 
> return 0;
> 
> > +}
> > +#else
> > +static inline int pmc_core_dbgfs_register(struct pmc_dev *pmc)
> > +{
> > +       return 0; /* nothing to register */
> > +}
> > +
> 
> > +static inline void pmc_core_dbgfs_unregister(struct pmc_dev *pmc)
> > +{
> > +       /* nothing to deregister */
> > +}
> 
> Redundant.
> 

Same as above.

> > +#endif /* CONFIG_DEBUG_FS */
> > +
> > +static const struct x86_cpu_id intel_pmc_core_ids[] = {
> > +       { X86_VENDOR_INTEL, 6, 0x4e, X86_FEATURE_MWAIT,
> > +               (kernel_ulong_t)NULL}, /* Skylake CPUID Signature */
> 
> No explicit NULL.
> 

Same as explained above.

> > +       { X86_VENDOR_INTEL, 6, 0x5e, X86_FEATURE_MWAIT,
> > +               (kernel_ulong_t)NULL}, /* Skylake CPUID Signature */
> 
> Ditto.
> 

Same as explained above.

> > +       {}
> > +};
> > +MODULE_DEVICE_TABLE(x86cpu, intel_pmc_core_ids);
> > +
> > +static int pmc_core_probe(struct pci_dev *dev, const struct pci_device_id *id)
> > +{
> 
> > +       int err;
> > +       const struct x86_cpu_id *cpu_id;
> 
> Swap them.
> 
>  +       const struct x86_cpu_id *cpu_id;
>  +       int err;
> 
> struct pmc_dev *pmcdev = &pmc;
>

Ok.
 
> > +
> > +       cpu_id = x86_match_cpu(intel_pmc_core_ids);
> > +       if (!cpu_id) {
> > +               err = -EINVAL;
> > +               goto exit;
> > +       }
> > +
> > +       err = pci_enable_device(dev);
> 
> pcim_enable_device();
> 

Thanks for this suggestion.

> > +       if (err) {
> > +               dev_err(&dev->dev, "PMC Core: failed to enable Power Management Controller.\n");
> 
> I doubt this message is useful anyhow.
> 
> > +               goto exit;
> > +       }
> > +
> > +       err = pci_read_config_dword(dev,
> > +                                   SPT_PMC_BASE_ADDR_OFFSET,
> > +                                   &pmc.base_addr);
> 
> 'pmc.' -> 'pmcdev->'
> 
> > +       if (err) {
> > +               dev_err(&dev->dev, "PMC Core: failed to read pci config space.\n");
> > +               goto disable_pci;
> > +       }
> 
> So, and this is not available through BARs?
> 
> > +       dev_dbg(&dev->dev, "PMC Core: PWRMBASE is 0x%x\n", pmc.base_addr);
> 
> %#x will prefix the number.
> 
> > +

Ok.

> > +       pmc.regmap = ioremap_nocache(pmc.base_addr, SPT_PMC_MMIO_REG_LEN);
> > +       if (!pmc.regmap) {
> 
> > +               dev_err(&dev->dev, "PMC Core: ioremap failed\n");
> 
> Useful?
> 

Want to keep it for debug purpose. 
Do you recommend devm_ioremap_nocache as well?

> > +               err = -ENOMEM;
> > +               goto disable_pci;
> > +       }
> > +
> > +       err = pmc_core_dbgfs_register(&pmc);
> > +       if (err) {
> > +               dev_err(&dev->dev, "PMC Core: debugfs register failed\n");
> > +               iounmap(pmc.regmap);
> > +               goto disable_pci;Do you recommend devm_ioremap_nocache as well?
> > +       }
> > +
> > +       pmc.has_slp_s0_res = true;
> 
> 
> > +       return 0;
> > +
> 
> > +disable_pci:
> > +       pci_disable_device(dev);
> 
> Remove after using pcim_*().
> 

Ok.

> > +exit:
> 
> Redundant. Use return directly.
> 

Ok.

> > +       return err;
> > +}
> > +
> > +static void intel_pmc_core_remove(struct pci_dev *pdev)
> > +{
> > +       pmc_core_dbgfs_unregister(&pmc);
> > +       pci_disable_device(pdev);
> > +       iounmap(pmc.regmap);
> > +}
> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko

-- 
Best Regards,
Rajneesh

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