Re: [PATCH] mailbox: pcc: Support HW-Reduced Communication Subspace Type 2

[Alexey Klimov <alexey.klimov@arm.com>]

Hi Hoan,

On Tue, Apr 5, 2016 at 11:14 PM, hotran <hotran@apm.com> wrote:
> ACPI 6.1 has a HW-Reduced Communication Subspace Type 2 intended for
> use on HW-Reduce ACPI Platform, which requires read-modify-write sequence
> to acknowledge doorbell interrupt. This patch provides the implementation
> for the Communication Subspace Type 2.
>
> Signed-off-by: Hoan Tran <hotran@apm.com>
> ---
>  drivers/mailbox/pcc.c | 384 +++++++++++++++++++++++++++++++++++++-------------
>  include/acpi/actbl3.h |   8 +-
>  2 files changed, 294 insertions(+), 98 deletions(-)
>
> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> index 0ddf638..4ed8153 100644
> --- a/drivers/mailbox/pcc.c
> +++ b/drivers/mailbox/pcc.c
> @@ -59,6 +59,7 @@
>  #include <linux/delay.h>
>  #include <linux/io.h>
>  #include <linux/init.h>
> +#include <linux/interrupt.h>
>  #include <linux/list.h>
>  #include <linux/platform_device.h>
>  #include <linux/mailbox_controller.h>
> @@ -68,27 +69,178 @@
>  #include "mailbox.h"
>
>  #define MAX_PCC_SUBSPACES      256
> +#define MBOX_IRQ_NAME          "pcc-mbox"
>
> -static struct mbox_chan *pcc_mbox_channels;
> +/**
> + * PCC mailbox channel information
> + *
> + * @chan:      Pointer to mailbox communication channel
> + * @pcc_doorbell_vaddr: PCC doorbell register address
> + * @pcc_doorbell_ack_vaddr: PCC doorbell ack register address
> + * @irq:       Interrupt number of the channel
> + */
> +struct pcc_mbox_chan {
> +       struct mbox_chan        *chan;
> +       void __iomem            *pcc_doorbell_vaddr;
> +       void __iomem            *pcc_doorbell_ack_vaddr;
> +       int                     irq;
> +};
>
> -/* Array of cached virtual address for doorbell registers */
> -static void __iomem **pcc_doorbell_vaddr;
> +/**
> + * PCC mailbox controller data
> + *
> + * @mb_ctrl:   Representation of the communication channel controller
> + * @mbox_chan: Array of PCC mailbox channels of the controller
> + * @chans:     Array of mailbox communication channels
> + */
> +struct pcc_mbox {
> +       struct mbox_controller  mbox_ctrl;
> +       struct pcc_mbox_chan    *mbox_chans;
> +       struct mbox_chan        *chans;
> +};
> +
> +static struct pcc_mbox pcc_mbox_ctx = {};
>
> -static struct mbox_controller pcc_mbox_ctrl = {};
>  /**
>   * get_pcc_channel - Given a PCC subspace idx, get
> - *     the respective mbox_channel.
> + *     the respective pcc mbox_channel.
>   * @id: PCC subspace index.
>   *
>   * Return: ERR_PTR(errno) if error, else pointer
> - *     to mbox channel.
> + *     to pcc mbox channel.
>   */
> -static struct mbox_chan *get_pcc_channel(int id)
> +static struct pcc_mbox_chan *get_pcc_channel(int id)
>  {
> -       if (id < 0 || id > pcc_mbox_ctrl.num_chans)
> +       if (id < 0 || id > pcc_mbox_ctx.mbox_ctrl.num_chans)
>                 return ERR_PTR(-ENOENT);
>
> -       return &pcc_mbox_channels[id];
> +       return &pcc_mbox_ctx.mbox_chans[id];
> +}
> +
> +/*
> + * PCC can be used with perf critical drivers such as CPPC
> + * So it makes sense to locally cache the virtual address and
> + * use it to read/write to PCC registers such as doorbell register
> + *
> + * The below read_register and write_registers are used to read and
> + * write from perf critical registers such as PCC doorbell register
> + */
> +static int read_register(void __iomem *vaddr, u64 *val, unsigned int bit_width)
> +{
> +       int ret_val = 0;
> +
> +       switch (bit_width) {
> +       case 8:
> +               *val = readb(vaddr);
> +               break;
> +       case 16:
> +               *val = readw(vaddr);
> +               break;
> +       case 32:
> +               *val = readl(vaddr);
> +               break;
> +       case 64:
> +               *val = readq(vaddr);
> +               break;
> +       default:
> +               pr_debug("Error: Cannot read register of %u bit width",
> +                       bit_width);
> +               ret_val = -EFAULT;
> +               break;
> +       }
> +       return ret_val;
> +}
> +
> +static int write_register(void __iomem *vaddr, u64 val, unsigned int bit_width)
> +{
> +       int ret_val = 0;
> +
> +       switch (bit_width) {
> +       case 8:
> +               writeb(val, vaddr);
> +               break;
> +       case 16:
> +               writew(val, vaddr);
> +               break;
> +       case 32:
> +               writel(val, vaddr);
> +               break;
> +       case 64:
> +               writeq(val, vaddr);
> +               break;
> +       default:
> +               pr_debug("Error: Cannot write register of %u bit width",
> +                       bit_width);
> +               ret_val = -EFAULT;
> +               break;
> +       }
> +       return ret_val;
> +}
> +
> +/**
> + * pcc_map_interrupt - Map a PCC subspace GSI to a linux IRQ number
> + * @interrupt: GSI number.
> + * @flags: interrupt flags
> + *
> + * Returns: a valid linux IRQ number on success
> + *             0 or -EINVAL on failure
> + */
> +static int pcc_map_interrupt(u32 interrupt, u32 flags)
> +{
> +       int trigger, polarity;
> +
> +       if (!interrupt)
> +               return 0;
> +
> +       trigger = (flags & ACPI_PCCT_INTERRUPT_MODE) ? ACPI_EDGE_SENSITIVE
> +                       : ACPI_LEVEL_SENSITIVE;
> +
> +       polarity = (flags & ACPI_PCCT_INTERRUPT_POLARITY) ? ACPI_ACTIVE_LOW
> +                       : ACPI_ACTIVE_HIGH;
> +
> +       return acpi_register_gsi(NULL, interrupt, trigger, polarity);
> +}
> +
> +/**
> + * pcc_mbox_irq - PCC mailbox interrupt handler
> + */
> +static irqreturn_t pcc_mbox_irq(int irq, void *id)
> +{
> +       struct acpi_generic_address *doorbell_ack;
> +       struct acpi_pcct_hw_reduced *pcct_ss;
> +       struct pcc_mbox_chan *pcc_chan = id;
> +       u64 doorbell_ack_preserve;
> +       struct mbox_chan *chan;
> +       u64 doorbell_ack_write;
> +       u64 doorbell_ack_val;
> +       int ret = 0;

Could you please check that you really need this initialization?

> +       chan = pcc_chan->chan;
> +       pcct_ss = chan->con_priv;
> +
> +       /* Clear interrupt status */
> +       if (pcct_ss->header.type == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2) {
> +               doorbell_ack = &pcct_ss->doorbell_ack_register;
> +               doorbell_ack_preserve = pcct_ss->ack_preserve_mask;
> +               doorbell_ack_write = pcct_ss->ack_write_mask;
> +
> +               ret = read_register(pcc_chan->pcc_doorbell_ack_vaddr,
> +                                   &doorbell_ack_val,
> +                                   doorbell_ack->bit_width);
> +               if (ret)
> +                       return ret;
> +
> +               ret = write_register(pcc_chan->pcc_doorbell_ack_vaddr,
> +                                    (doorbell_ack_val & doorbell_ack_preserve)
> +                                       | doorbell_ack_write,
> +                                    doorbell_ack->bit_width);
> +               if (ret)
> +                       return ret;

Could you please check that really need to return -EFAULT here in case of error?
Looking through irqreturn values it looks like IRQ_NONE is more proper value.


> +       }
> +
> +       mbox_chan_received_data(chan, NULL);
> +
> +       return IRQ_HANDLED;
>  }
>

[...]

>  /**
> + * pcc_parse_subspace_irq - Parse the PCC IRQ and PCC ACK register
> + *             There should be one entry per PCC client.
> + * @mbox_chans: Pointer to the PCC mailbox channel data
> + * @pcct_ss: Pointer to the ACPI subtable header under the PCCT.
> + *
> + * Return: 0 for Success, else errno.
> + *
> + * This gets called for each entry in the PCC table.
> + */
> +static int pcc_parse_subspace_irq(struct pcc_mbox_chan *mbox_chans,
> +               struct acpi_pcct_hw_reduced *pcct_ss)
> +{
> +       mbox_chans->irq = pcc_map_interrupt(pcct_ss->doorbell_interrupt,
> +                                           (u32)pcct_ss->flags);
> +       if (mbox_chans->irq <= 0) {
> +               pr_err("PCC GSI %d not registered\n",
> +                      pcct_ss->doorbell_interrupt);
> +               return -EINVAL;
> +       }
> +
> +       if (pcct_ss->header.type
> +               == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2) {
> +               mbox_chans->pcc_doorbell_ack_vaddr = acpi_os_ioremap(
> +                               pcct_ss->doorbell_ack_register.address,
> +                               pcct_ss->doorbell_ack_register.bit_width / 8);
> +               if (!mbox_chans->pcc_doorbell_ack_vaddr) {
> +                       pr_err("Failed to ioremap PCC ACK register\n");
> +                       return -ENOMEM;
> +               }
> +       }
> +
> +       return 0;
> +}
> +
> +/**
>   * acpi_pcc_probe - Parse the ACPI tree for the PCCT.
>   *
>   * Return: 0 for Success, else errno.
> @@ -316,7 +479,8 @@ static int __init acpi_pcc_probe(void)
>         acpi_size pcct_tbl_header_size;
>         struct acpi_table_header *pcct_tbl;
>         struct acpi_subtable_header *pcct_entry;
> -       int count, i;
> +       struct acpi_table_pcct *acpi_pcct_tbl;
> +       int count, i, rc;
>         acpi_status status = AE_OK;
>
>         /* Search for PCCT */
> @@ -335,21 +499,29 @@ static int __init acpi_pcc_probe(void)
>                         parse_pcc_subspace, MAX_PCC_SUBSPACES);
>
>         if (count <= 0) {
> +               count = acpi_table_parse_entries(ACPI_SIG_PCCT,
> +                               sizeof(struct acpi_table_pcct),
> +                               ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2,
> +                               parse_pcc_subspace, MAX_PCC_SUBSPACES);
> +       }
> +
> +       if (count <= 0) {

Do I understand this change correctly: in case type1 is present code flow doesn't try to parse type2 tables?
Is presence of both type2 and type1 prohibited by specs?

>                 pr_err("Error parsing PCC subspaces from PCCT\n");
>                 return -EINVAL;
>         }

[...]

Best regards,
Alexey