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Commit 8b0f5788 authored by Prakash, Prashanth's avatar Prakash, Prashanth Committed by Rafael J. Wysocki
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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: default avatarPrashanth Prakash <pprakash@codeaurora.org>
Acked-by: default avatarAshwin Chaugule <ashwin.chaugule@linaro.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 77e3d86f

drivers/mailbox/pcc.c

+104 −7
Original line number Diff line number Diff line
@@ -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;