linux-kernel - Re: [PATCH v3 1/4] PCI: pciehp: Add pciehp_set_indicators() to jointly set LED indicators

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Date:   Wed, 28 Aug 2019 09:41:59 +1000
From:   "Oliver O'Halloran" <oohall@...il.com>
To:     Denis Efremov <efremov@...ux.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Lukas Wunner <lukas@...ner.de>,
        sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] PCI: pciehp: Add pciehp_set_indicators() to
 jointly set LED indicators

On Tue, Aug 20, 2019 at 2:07 AM Denis Efremov <efremov@...ux.com> wrote:
>
> Add pciehp_set_indicators() to set power and attention indicators with a
> single register write. Thus, avoiding waiting twice for Command Complete.
>
> Signed-off-by: Denis Efremov <efremov@...ux.com>
> ---
>  drivers/pci/hotplug/pciehp.h     |  1 +
>  drivers/pci/hotplug/pciehp_hpc.c | 29 +++++++++++++++++++++++++++++
>  include/uapi/linux/pci_regs.h    |  2 ++
>  3 files changed, 32 insertions(+)
>
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index 8c51a04b8083..0e272bf3deb4 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -167,6 +167,7 @@ int pciehp_power_on_slot(struct controller *ctrl);
>  void pciehp_power_off_slot(struct controller *ctrl);
>  void pciehp_get_power_status(struct controller *ctrl, u8 *status);
>
> +void pciehp_set_indicators(struct controller *ctrl, int pwr, int attn);
>  void pciehp_set_attention_status(struct controller *ctrl, u8 status);
>  void pciehp_get_latch_status(struct controller *ctrl, u8 *status);
>  int pciehp_query_power_fault(struct controller *ctrl);
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index bd990e3371e3..5474b9854a7f 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -443,6 +443,35 @@ void pciehp_set_attention_status(struct controller *ctrl, u8 value)
>                  pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, slot_cmd);
>  }
>
> +void pciehp_set_indicators(struct controller *ctrl, int pwr, int attn)
> +{
> +       u16 cmd = 0, mask = 0;
> +
> +       if (PWR_LED(ctrl))
> +               switch (pwr) {
> +               case PCI_EXP_SLTCTL_PWR_IND_ON:
> +               case PCI_EXP_SLTCTL_PWR_IND_BLINK:
> +               case PCI_EXP_SLTCTL_PWR_IND_OFF:

Do you need an explicit /* fallthrough */ comment? I thought the
fallthrough warning was enabled by default now.

> +                       cmd |= pwr;
> +                       mask |= PCI_EXP_SLTCTL_PIC;
> +               }
> +
> +       if (ATTN_LED(ctrl))
> +               switch (attn) {
> +               case PCI_EXP_SLTCTL_ATTN_IND_ON:
> +               case PCI_EXP_SLTCTL_ATTN_IND_BLINK:
> +               case PCI_EXP_SLTCTL_ATTN_IND_OFF:
> +                       cmd |= attn;
> +                       mask |= PCI_EXP_SLTCTL_AIC;
> +               }
> +
> +       if (cmd) {
> +               pcie_write_cmd_nowait(ctrl, cmd, mask);
> +               ctrl_dbg(ctrl, "%s: SLOTCTRL %x write cmd %x\n", __func__,
> +                        pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, cmd);
> +       }
> +}
> +
>  void pciehp_green_led_on(struct controller *ctrl)
>  {
>         if (!PWR_LED(ctrl))
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index f28e562d7ca8..291788b58f3a 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -591,10 +591,12 @@
>  #define  PCI_EXP_SLTCTL_CCIE   0x0010  /* Command Completed Interrupt Enable */
>  #define  PCI_EXP_SLTCTL_HPIE   0x0020  /* Hot-Plug Interrupt Enable */
>  #define  PCI_EXP_SLTCTL_AIC    0x00c0  /* Attention Indicator Control */

> +#define  PCI_EXP_SLTCTL_ATTN_IND_NONE  0x0    /* Attention Indicator noop */
>  #define  PCI_EXP_SLTCTL_ATTN_IND_ON    0x0040 /* Attention Indicator on */
>  #define  PCI_EXP_SLTCTL_ATTN_IND_BLINK 0x0080 /* Attention Indicator blinking */
>  #define  PCI_EXP_SLTCTL_ATTN_IND_OFF   0x00c0 /* Attention Indicator off */
>  #define  PCI_EXP_SLTCTL_PIC    0x0300  /* Power Indicator Control */
> +#define  PCI_EXP_SLTCTL_PWR_IND_NONE   0x0    /* Power Indicator noop */

I don't think pci_regs.h is the right place for this. The contents of
pci_regs.h is essentially a transcription of bit definitions from the
various PCI standards documents. The PCIe Base spec says the the 0b00
combination for the two-bit Power and Attn indicator fields is
reserved and there's nothing suggesting that writing a zero to those
fields should preserve the current value. Basicly, we now have a
implementation quirk of pcie_set_indicators() masquerading as part of
the standard.

>  #define  PCI_EXP_SLTCTL_PWR_IND_ON     0x0100 /* Power Indicator on */
>  #define  PCI_EXP_SLTCTL_PWR_IND_BLINK  0x0200 /* Power Indicator blinking */
>  #define  PCI_EXP_SLTCTL_PWR_IND_OFF    0x0300 /* Power Indicator off */
> --
> 2.21.0
>