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mailbox: pcc: optimized pcc_send_data 

pcc_send_data() can be invoked during the execution of performance
critical code as in cppc_cpufreq driver. With acpi_* APIs, the
doorbell register accessed in pcc_send_data() if present in system
memory will be searched (in cached virt to phys addr mapping),
mapped, read/written and then unmapped. These operations take
significant amount of time.

This patch maps the performance critical doorbell register
during init and then reads/writes to it directly using the
mapped virtual address. This patch + similar changes to CPPC
acpi driver reduce the time per freq. transition from around
200us to about 20us for the CPPC cpufreq driver

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
Acked-by: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Prakash, Prashanth 2016-02-17 13:21:01 -07:00 committed by Rafael J. Wysocki
parent 77e3d86f2f
commit 8b0f578898
1 changed files with 104 additions and 7 deletions
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111
drivers/mailbox/pcc.c
View File

@ -63,6 +63,7 @@
#include <linux/platform_device.h>
#include <linux/mailbox_controller.h>
#include <linux/mailbox_client.h>
#include <linux/io-64-nonatomic-lo-hi.h>
#include "mailbox.h"
@ -70,6 +71,9 @@
static struct mbox_chan *pcc_mbox_channels;
/* Array of cached virtual address for doorbell registers */
static void __iomem **pcc_doorbell_vaddr;
static struct mbox_controller pcc_mbox_ctrl = {};
/**
* get_pcc_channel - Given a PCC subspace idx, get
@ -166,6 +170,66 @@ void pcc_mbox_free_channel(struct mbox_chan *chan)
}
EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);
/*
* 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_send_data - Called from Mailbox Controller code. Used
* here only to ring the channel doorbell. The PCC client
@ -181,21 +245,39 @@ EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);
static int pcc_send_data(struct mbox_chan *chan, void *data)
{
struct acpi_pcct_hw_reduced *pcct_ss = chan->con_priv;
struct acpi_generic_address doorbell;
struct acpi_generic_address *doorbell;
u64 doorbell_preserve;
u64 doorbell_val;
u64 doorbell_write;
u32 id = chan - pcc_mbox_channels;
int ret = 0;
doorbell = pcct_ss->doorbell_register;
if (id >= pcc_mbox_ctrl.num_chans) {
pr_debug("pcc_send_data: Invalid mbox_chan passed\n");
return -ENOENT;
}
doorbell = &pcct_ss->doorbell_register;
doorbell_preserve = pcct_ss->preserve_mask;
doorbell_write = pcct_ss->write_mask;
/* Sync notification from OS to Platform. */
acpi_read(&doorbell_val, &doorbell);
acpi_write((doorbell_val & doorbell_preserve) | doorbell_write,
&doorbell);
return 0;
if (pcc_doorbell_vaddr[id]) {
ret = read_register(pcc_doorbell_vaddr[id], &doorbell_val,
doorbell->bit_width);
if (ret)
return ret;
ret = write_register(pcc_doorbell_vaddr[id],
(doorbell_val & doorbell_preserve) | doorbell_write,
doorbell->bit_width);
} else {
ret = acpi_read(&doorbell_val, doorbell);
if (ret)
return ret;
ret = acpi_write((doorbell_val & doorbell_preserve) | doorbell_write,
doorbell);
}
return ret;
}
static const struct mbox_chan_ops pcc_chan_ops = {
@ -271,14 +353,29 @@ static int __init acpi_pcc_probe(void)
return -ENOMEM;
}
pcc_doorbell_vaddr = kcalloc(count, sizeof(void *), GFP_KERNEL);
if (!pcc_doorbell_vaddr) {
kfree(pcc_mbox_channels);
return -ENOMEM;
}
/* Point to the first PCC subspace entry */
pcct_entry = (struct acpi_subtable_header *) (
(unsigned long) pcct_tbl + sizeof(struct acpi_table_pcct));
for (i = 0; i < count; i++) {
struct acpi_generic_address *db_reg;
struct acpi_pcct_hw_reduced *pcct_ss;
pcc_mbox_channels[i].con_priv = pcct_entry;
pcct_entry = (struct acpi_subtable_header *)
((unsigned long) pcct_entry + pcct_entry->length);
/* If doorbell is in system memory cache the virt address */
pcct_ss = (struct acpi_pcct_hw_reduced *)pcct_entry;
db_reg = &pcct_ss->doorbell_register;
if (db_reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
pcc_doorbell_vaddr[i] = acpi_os_ioremap(db_reg->address,
db_reg->bit_width/8);
}
pcc_mbox_ctrl.num_chans = count;