Re: [PATCH v3 1/1] x86/platform/intel-mid: Retrofit pci_platform_pm_ops ->get_state hook

[Bryan O'Donoghue <pure.logic@nexus-software.ie>]

On Sun, 2016-10-23 at 13:55 +0200, Lukas Wunner wrote:
> Commit cc7cc02bada8 ("PCI: Query platform firmware for device power
> state") augmented struct pci_platform_pm_ops with a ->get_state hook
> and
> implemented it for acpi_pci_platform_pm, the only pci_platform_pm_ops
> existing till v4.7.
> 
> However v4.8 introduced another pci_platform_pm_ops for Intel Mobile
> Internet Devices with commit 5823d0893ec2 ("x86/platform/intel-mid:
> Add
> Power Management Unit driver").  It is missing the ->get_state hook,
> which is fatal since pci_set_platform_pm() enforces its
> presence.  Andy
> Shevchenko reports that without the present commit, such a device
> "crashes without even a character printed out on serial console and
> reboots (since watchdog)".
> 
> Retrofit mid_pci_platform_pm with the missing callback to fix the
> breakage.
> 
> Fixes: cc7cc02bada8 ("PCI: Query platform firmware for device power
> state")
> Cc: x86@kernel.org
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Acked-and-tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.c
> om>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
> Changes v1 -> v2:
> - Cast return value of intel_mid_pci_get_power_state() to
>   (__force pci_power_t) to avoid "sparse -D__CHECK_ENDIAN__" warning.
> - Add ack by Andy Shevchenko.
> 
> Changes v2 -> v3:
> - Amend commit message to explain the user-visible failure mode as
>   reported by Andy.
> - Add ack by Bjorn Helgaas and Fixes tag.
> 
>  arch/x86/include/asm/intel-mid.h  |  1 +
>  arch/x86/platform/intel-mid/pwr.c | 19 +++++++++++++++++++
>  drivers/pci/pci-mid.c             |  6 ++++++
>  3 files changed, 26 insertions(+)
> 
> diff --git a/arch/x86/include/asm/intel-mid.h
> b/arch/x86/include/asm/intel-mid.h
> index 5b6753d..49da9f4 100644
> --- a/arch/x86/include/asm/intel-mid.h
> +++ b/arch/x86/include/asm/intel-mid.h
> @@ -17,6 +17,7 @@
>  
>  extern int intel_mid_pci_init(void);
>  extern int intel_mid_pci_set_power_state(struct pci_dev *pdev,
> pci_power_t state);
> +extern pci_power_t intel_mid_pci_get_power_state(struct pci_dev
> *pdev);
>  
>  extern void intel_mid_pwr_power_off(void);
>  
> diff --git a/arch/x86/platform/intel-mid/pwr.c
> b/arch/x86/platform/intel-mid/pwr.c
> index 5d3b45a..67375dd 100644
> --- a/arch/x86/platform/intel-mid/pwr.c
> +++ b/arch/x86/platform/intel-mid/pwr.c
> @@ -272,6 +272,25 @@ int intel_mid_pci_set_power_state(struct pci_dev
> *pdev, pci_power_t state)
>  }
>  EXPORT_SYMBOL_GPL(intel_mid_pci_set_power_state);
>  
> +pci_power_t intel_mid_pci_get_power_state(struct pci_dev *pdev)
> +{
> +	struct mid_pwr *pwr = midpwr;
> +	int id, reg, bit;
> +	u32 power;
> +
> +	if (!pwr || !pwr->available)
> +		return PCI_UNKNOWN;
> +
> +	id = intel_mid_pwr_get_lss_id(pdev);
> +	if (id < 0)
> +		return PCI_UNKNOWN;
> +
> +	reg = (id * LSS_PWS_BITS) / 32;
> +	bit = (id * LSS_PWS_BITS) % 32;
> +	power = mid_pwr_get_state(pwr, reg);
> +	return (__force pci_power_t)((power >> bit) & 3);
> +}
> +
>  void intel_mid_pwr_power_off(void)
>  {
>  	struct mid_pwr *pwr = midpwr;
> diff --git a/drivers/pci/pci-mid.c b/drivers/pci/pci-mid.c
> index 55f453d..c7f3408 100644
> --- a/drivers/pci/pci-mid.c
> +++ b/drivers/pci/pci-mid.c
> @@ -29,6 +29,11 @@ static int mid_pci_set_power_state(struct pci_dev
> *pdev, pci_power_t state)
>  	return intel_mid_pci_set_power_state(pdev, state);
>  }
>  
> +static pci_power_t mid_pci_get_power_state(struct pci_dev *pdev)
> +{
> +	return intel_mid_pci_get_power_state(pdev);
> +}
> +
>  static pci_power_t mid_pci_choose_state(struct pci_dev *pdev)
>  {
>  	return PCI_D3hot;
> @@ -52,6 +57,7 @@ static bool mid_pci_need_resume(struct pci_dev
> *dev)
>  static struct pci_platform_pm_ops mid_pci_platform_pm = {
>  	.is_manageable	= mid_pci_power_manageable,
>  	.set_state	= mid_pci_set_power_state,
> +	.get_state	= mid_pci_get_power_state,
>  	.choose_state	= mid_pci_choose_state,
>  	.sleep_wake	= mid_pci_sleep_wake,
>  	.run_wake	= mid_pci_run_wake,

Shouldn't this serialize like this

        might_sleep();

	reg = (id * LSS_PWS_BITS) / 32;
	bit = (id * LSS_PWS_BITS) % 32;

        mutex_lock(&pwr->lock);
	power = mid_pwr_get_state(pwr, reg);
        mutex_lock(&pwr->lock);

	return (__force pci_power_t)((power >> bit) & 3);

there's a corresponding flow in mid_pwr_set_power_state() that operates
in exactly that way.

---
bod