#include <linux/cpufreq.h>
#include <linux/delay.h>
#include <linux/ktime.h>
+#include <linux/rwsem.h>
+#include <linux/wait.h>
#include <acpi/cppc_acpi.h>
+
/*
- * Lock to provide mutually exclusive access to the PCC
- * channel. e.g. When the remote updates the shared region
- * with new data, the reader needs to be protected from
- * other CPUs activity on the same channel.
+ * Lock to provide controlled access to the PCC channel.
+ *
+ * For performance critical usecases(currently cppc_set_perf)
+ * We need to take read_lock and check if channel belongs to OSPM before
+ * reading or writing to PCC subspace
+ * We need to take write_lock before transferring the channel ownership to
+ * the platform via a Doorbell
+ * This allows us to batch a number of CPPC requests if they happen to
+ * originate in about the same time
+ *
+ * For non-performance critical usecases(init)
+ * Take write_lock for all purposes which gives exclusive access
*/
-static DEFINE_SPINLOCK(pcc_lock);
+static DECLARE_RWSEM(pcc_lock);
+
+/* Indicates if there are any pending/batched PCC write commands */
+static bool pending_pcc_write_cmd;
+
+/* Wait queue for CPUs whose requests were batched */
+static DECLARE_WAIT_QUEUE_HEAD(pcc_write_wait_q);
+
+/* Used to identify if a batched request is delivered to platform */
+static unsigned int pcc_write_cnt;
/*
* The cpc_desc structure contains the ACPI register details
/* pcc mapped address + header size + offset within PCC subspace */
#define GET_PCC_VADDR(offs) (pcc_comm_addr + 0x8 + (offs))
+/* Check if a CPC regsiter is in PCC */
+#define CPC_IN_PCC(cpc) ((cpc)->type == ACPI_TYPE_BUFFER && \
+ (cpc)->cpc_entry.reg.space_id == \
+ ACPI_ADR_SPACE_PLATFORM_COMM)
+
/*
* Arbitrary Retries in case the remote processor is slow to respond
* to PCC commands. Keeping it high enough to cover emulators where
return ret;
}
+/*
+ * This function transfers the ownership of the PCC to the platform
+ * So it must be called while holding write_lock(pcc_lock)
+ */
static int send_pcc_cmd(u16 cmd)
{
- int ret = -EIO;
+ int ret = -EIO, i;
struct acpi_pcct_shared_memory *generic_comm_base =
(struct acpi_pcct_shared_memory *) pcc_comm_addr;
static ktime_t last_cmd_cmpl_time, last_mpar_reset;
* the channel before writing to PCC space
*/
if (cmd == CMD_READ) {
+ /*
+ * If there are pending cpc_writes, then we stole the channel
+ * before write completion, so first send a WRITE command to
+ * platform
+ */
+ if (pending_pcc_write_cmd)
+ send_pcc_cmd(CMD_WRITE);
+
ret = check_pcc_chan();
if (ret)
- return ret;
- }
+ goto end;
+ } else /* CMD_WRITE */
+ pending_pcc_write_cmd = FALSE;
/*
* Handle the Minimum Request Turnaround Time(MRTT)
time_delta = ktime_ms_delta(ktime_get(), last_mpar_reset);
if (time_delta < 60 * MSEC_PER_SEC) {
pr_debug("PCC cmd not sent due to MPAR limit");
- return -EIO;
+ ret = -EIO;
+ goto end;
}
last_mpar_reset = ktime_get();
mpar_count = pcc_mpar;
if (ret < 0) {
pr_err("Err sending PCC mbox message. cmd:%d, ret:%d\n",
cmd, ret);
- return ret;
+ goto end;
}
/*
}
mbox_client_txdone(pcc_channel, ret);
+
+end:
+ if (cmd == CMD_WRITE) {
+ if (unlikely(ret)) {
+ for_each_possible_cpu(i) {
+ struct cpc_desc *desc = per_cpu(cpc_desc_ptr, i);
+ if (!desc)
+ continue;
+
+ if (desc->write_cmd_id == pcc_write_cnt)
+ desc->write_cmd_status = ret;
+ }
+ }
+ pcc_write_cnt++;
+ wake_up_all(&pcc_write_wait_q);
+ }
+
return ret;
}
nom_perf = &cpc_desc->cpc_regs[NOMINAL_PERF];
/* Are any of the regs PCC ?*/
- if ((highest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
- (lowest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
- (ref_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
- (nom_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
- spin_lock(&pcc_lock);
+ if (CPC_IN_PCC(highest_reg) || CPC_IN_PCC(lowest_reg) ||
+ CPC_IN_PCC(ref_perf) || CPC_IN_PCC(nom_perf)) {
regs_in_pcc = 1;
+ down_write(&pcc_lock);
/* Ring doorbell once to update PCC subspace */
if (send_pcc_cmd(CMD_READ) < 0) {
ret = -EIO;
out_err:
if (regs_in_pcc)
- spin_unlock(&pcc_lock);
+ up_write(&pcc_lock);
return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_perf_caps);
reference_reg = &cpc_desc->cpc_regs[REFERENCE_CTR];
/* Are any of the regs PCC ?*/
- if ((delivered_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
- (reference_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
- spin_lock(&pcc_lock);
+ if (CPC_IN_PCC(delivered_reg) || CPC_IN_PCC(reference_reg)) {
+ down_write(&pcc_lock);
regs_in_pcc = 1;
/* Ring doorbell once to update PCC subspace */
if (send_pcc_cmd(CMD_READ) < 0) {
out_err:
if (regs_in_pcc)
- spin_unlock(&pcc_lock);
+ up_write(&pcc_lock);
return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);
desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
- /* If this is PCC reg, check if channel is free before writing */
- if (desired_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
- spin_lock(&pcc_lock);
- ret = check_pcc_chan();
- if (ret)
- goto busy_channel;
+ /*
+ * This is Phase-I where we want to write to CPC registers
+ * -> We want all CPUs to be able to execute this phase in parallel
+ *
+ * Since read_lock can be acquired by multiple CPUs simultaneously we
+ * achieve that goal here
+ */
+ if (CPC_IN_PCC(desired_reg)) {
+ down_read(&pcc_lock); /* BEGIN Phase-I */
+ /*
+ * If there are pending write commands i.e pending_pcc_write_cmd
+ * is TRUE, then we know OSPM owns the channel as another CPU
+ * has already checked for command completion bit and updated
+ * the corresponding CPC registers
+ */
+ if (!pending_pcc_write_cmd) {
+ ret = check_pcc_chan();
+ if (ret) {
+ up_read(&pcc_lock);
+ return ret;
+ }
+ /*
+ * Update the pending_write to make sure a PCC CMD_READ
+ * will not arrive and steal the channel during the
+ * transition to write lock
+ */
+ pending_pcc_write_cmd = TRUE;
+ }
+ cpc_desc->write_cmd_id = pcc_write_cnt;
+ cpc_desc->write_cmd_status = 0;
}
/*
*/
cpc_write(desired_reg, perf_ctrls->desired_perf);
- /* Is this a PCC reg ?*/
- if (desired_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
- /* Ring doorbell so Remote can get our perf request. */
- if (send_pcc_cmd(CMD_WRITE) < 0)
- ret = -EIO;
+ if (CPC_IN_PCC(desired_reg))
+ up_read(&pcc_lock); /* END Phase-I */
+ /*
+ * This is Phase-II where we transfer the ownership of PCC to Platform
+ *
+ * Short Summary: Basically if we think of a group of cppc_set_perf
+ * requests that happened in short overlapping interval. The last CPU to
+ * come out of Phase-I will enter Phase-II and ring the doorbell.
+ *
+ * We have the following requirements for Phase-II:
+ * 1. We want to execute Phase-II only when there are no CPUs
+ * currently executing in Phase-I
+ * 2. Once we start Phase-II we want to avoid all other CPUs from
+ * entering Phase-I.
+ * 3. We want only one CPU among all those who went through Phase-I
+ * to run phase-II
+ *
+ * If write_trylock fails to get the lock and doesn't transfer the
+ * PCC ownership to the platform, then one of the following will be TRUE
+ * 1. There is at-least one CPU in Phase-I which will later execute
+ * write_trylock, so the CPUs in Phase-I will be responsible for
+ * executing the Phase-II.
+ * 2. Some other CPU has beaten this CPU to successfully execute the
+ * write_trylock and has already acquired the write_lock. We know for a
+ * fact it(other CPU acquiring the write_lock) couldn't have happened
+ * before this CPU's Phase-I as we held the read_lock.
+ * 3. Some other CPU executing pcc CMD_READ has stolen the
+ * down_write, in which case, send_pcc_cmd will check for pending
+ * CMD_WRITE commands by checking the pending_pcc_write_cmd.
+ * So this CPU can be certain that its request will be delivered
+ * So in all cases, this CPU knows that its request will be delivered
+ * by another CPU and can return
+ *
+ * After getting the down_write we still need to check for
+ * pending_pcc_write_cmd to take care of the following scenario
+ * The thread running this code could be scheduled out between
+ * Phase-I and Phase-II. Before it is scheduled back on, another CPU
+ * could have delivered the request to Platform by triggering the
+ * doorbell and transferred the ownership of PCC to platform. So this
+ * avoids triggering an unnecessary doorbell and more importantly before
+ * triggering the doorbell it makes sure that the PCC channel ownership
+ * is still with OSPM.
+ * pending_pcc_write_cmd can also be cleared by a different CPU, if
+ * there was a pcc CMD_READ waiting on down_write and it steals the lock
+ * before the pcc CMD_WRITE is completed. pcc_send_cmd checks for this
+ * case during a CMD_READ and if there are pending writes it delivers
+ * the write command before servicing the read command
+ */
+ if (CPC_IN_PCC(desired_reg)) {
+ if (down_write_trylock(&pcc_lock)) { /* BEGIN Phase-II */
+ /* Update only if there are pending write commands */
+ if (pending_pcc_write_cmd)
+ send_pcc_cmd(CMD_WRITE);
+ up_write(&pcc_lock); /* END Phase-II */
+ } else
+ /* Wait until pcc_write_cnt is updated by send_pcc_cmd */
+ wait_event(pcc_write_wait_q,
+ cpc_desc->write_cmd_id != pcc_write_cnt);
+
+ /* send_pcc_cmd updates the status in case of failure */
+ ret = cpc_desc->write_cmd_status;
}
-busy_channel:
- if (desired_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)
- spin_unlock(&pcc_lock);
return ret;
}
EXPORT_SYMBOL_GPL(cppc_set_perf);
projects / platform / kernel / linux-rpi.git / commitdiff