On Fri, Jan 22, 2016 at 7:07 PM, Prashanth Prakash
<pprakash@xxxxxxxxxxxxxx> wrote:
> 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 cppc cpufreq driver
>
> Signed-off-by: Prashanth Prakash <pprakash@xxxxxxxxxxxxxx>
> Acked-by: Ashwin Chaugule <ashwin.chaugule@xxxxxxxxxx>
> ---
> drivers/mailbox/pcc.c | 111 ++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 104 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> index 45d85ae..050c206 100644
> --- a/drivers/mailbox/pcc.c
> +++ b/drivers/mailbox/pcc.c
> @@ -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 **pcc_doorbell_vaddr;
I think this needs to be
static void __iomem **pcc_doorbell_vaddr.
You really should use the 'sparse' tool on your patches to make sure
that you have correct __iomem usage. Pointers that are passed to
readl() and writel() should be __iomem pointers, and they should be
allocated with ioremap(). However, I noticed that you're not doing
that:
> +
> 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 *vaddr, u64 *val, unsigned int bit_width)
Once again, this should be "void __iomem *vaddr".
> +{
> + int ret_val = 0;
> +
> + switch (bit_width) {
> + case 8:
> + *val = readb(vaddr);
Remember, functions like readb(), writeb(), readl(), writel(), etc,
should only be used on pointers allocated via ioremap(), however ...
> + 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 *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;
> +
> + 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 = &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);
... this is wrong. You're using readl() and writel() on this pointer,
but it's not an iomem pointer, it's normal kernel memory. You need to
delete your usage of readX, writeX on this pointer.
> + 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;
> --
> Qualcomm Technologies, Inc. on behalf
> of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc.
> is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
>
> _______________________________________________
> Linaro-acpi mailing list
> Linaro-acpi@xxxxxxxxxxxxxxxx
> https://lists.linaro.org/mailman/listinfo/linaro-acpi
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
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