From: Ashwin Chaugule ashwin.chaugule@linaro.org
Previously the send_pcc_cmd() code checked if the PCC operation had completed before returning from the function. This check was performed regardless of the PCC op type (i.e. Read/Write). Knowing the type of cmd can be used to optimize the check and avoid needless waiting. e.g. with Write ops, the actual Writing is done before calling send_pcc_cmd(). And the subsequent Writes will check if the channel is free at the entry of send_pcc_cmd() anyway.
However, for Read cmds, we need to wait for the cmd completion bit to be flipped, since the actual Read ops follow after returning from the send_pcc_cmd(). So, only do the looping check at the end for Read ops.
Also, instead of using udelay() calls, use ktime as a means to check for deadlines. The current deadline in which the Remote should flip the cmd completion bit is defined as N * Nominal latency. Where N is arbitrary and large enough to work on slow emulators and Nominal latency comes from the ACPI table (PCCT). This helps in working around the CONFIG_HZ effects on udelay() and also avoids needing different ACPI tables for Silicon and Emulation platforms.
Signed-off-by: Ashwin Chaugule ashwin.chaugule@linaro.org Signed-off-by: Prashanth Prakash pprakash@codeaurora.org --- drivers/acpi/cppc_acpi.c | 102 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 74 insertions(+), 28 deletions(-)
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index 6730f96..36c3e4d 100644 --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -39,6 +39,7 @@
#include <linux/cpufreq.h> #include <linux/delay.h> +#include <linux/ktime.h>
#include <acpi/cppc_acpi.h> /* @@ -63,25 +64,56 @@ static struct mbox_chan *pcc_channel; static void __iomem *pcc_comm_addr; static u64 comm_base_addr; static int pcc_subspace_idx = -1; -static u16 pcc_cmd_delay; static bool pcc_channel_acquired; +static ktime_t deadline;
/* * Arbitrary Retries in case the remote processor is slow to respond - * to PCC commands. + * to PCC commands. Keeping it high enough to cover emulators where + * the processors run painfully slow. */ #define NUM_RETRIES 500
+static int check_pcc_chan(void) +{ + int result = -EIO; + struct acpi_pcct_shared_memory *generic_comm_base = + (struct acpi_pcct_shared_memory *) pcc_comm_addr; + ktime_t next_deadline = ktime_add(ktime_get(), deadline); + int retries = 0; + + /* Retry in case the remote processor was too slow to catch up. */ + while (!ktime_after(ktime_get(), next_deadline)) { + if (readw_relaxed(&generic_comm_base->status) & PCC_CMD_COMPLETE) { + result = 0; + break; + } + /* + * Reducing the bus traffic in case this loop takes longer than + * a few retries. + */ + udelay(3); + retries++; + } + + return result; +} + static int send_pcc_cmd(u16 cmd) { - int retries, result = -EIO; - struct acpi_pcct_hw_reduced *pcct_ss = pcc_channel->con_priv; + int ret = -EIO; struct acpi_pcct_shared_memory *generic_comm_base = (struct acpi_pcct_shared_memory *) pcc_comm_addr; - u32 cmd_latency = pcct_ss->latency;
- /* Min time OS should wait before sending next command. */ - udelay(pcc_cmd_delay); + /* + * For CMD_WRITE we know for a fact the caller should have checked + * the channel before writing to PCC space + */ + if (cmd == CMD_READ) { + ret = check_pcc_chan(); + if (ret) + return ret; + }
/* Write to the shared comm region. */ writew(cmd, &generic_comm_base->command); @@ -90,26 +122,25 @@ static int send_pcc_cmd(u16 cmd) writew(0, &generic_comm_base->status);
/* Ring doorbell */ - result = mbox_send_message(pcc_channel, &cmd); - if (result < 0) { + ret = mbox_send_message(pcc_channel, &cmd); + if (ret < 0) { pr_err("Err sending PCC mbox message. cmd:%d, ret:%d\n", - cmd, result); - return result; + cmd, ret); + return ret; }
- /* Wait for a nominal time to let platform process command. */ - udelay(cmd_latency); - - /* Retry in case the remote processor was too slow to catch up. */ - for (retries = NUM_RETRIES; retries > 0; retries--) { - if (readw_relaxed(&generic_comm_base->status) & PCC_CMD_COMPLETE) { - result = 0; - break; - } - } + /* + * For READs we need to ensure the cmd completed to ensure + * the ensuing read()s can proceed. For WRITEs we dont care + * because the actual write()s are done before coming here + * and the next READ or WRITE will check if the channel + * is busy/free at the entry of this call. + */ + if (cmd == CMD_READ) + ret = check_pcc_chan();
- mbox_client_txdone(pcc_channel, result); - return result; + mbox_client_txdone(pcc_channel, ret); + return ret; }
static void cppc_chan_tx_done(struct mbox_client *cl, void *msg, int ret) @@ -306,6 +337,7 @@ static int register_pcc_channel(int pcc_subspace_idx) { struct acpi_pcct_hw_reduced *cppc_ss; unsigned int len; + u64 usecs_lat;
if (pcc_subspace_idx >= 0) { pcc_channel = pcc_mbox_request_channel(&cppc_mbox_cl, @@ -335,7 +367,14 @@ static int register_pcc_channel(int pcc_subspace_idx) */ comm_base_addr = cppc_ss->base_address; len = cppc_ss->length; - pcc_cmd_delay = cppc_ss->min_turnaround_time; + + /* + * cppc_ss->latency is just a Nominal value. In reality + * the remote processor could be much slower to reply. + * So add an arbitrary amount of wait on top of Nominal. + */ + usecs_lat = NUM_RETRIES * cppc_ss->latency; + deadline = ns_to_ktime(usecs_lat * NSEC_PER_USEC);
pcc_comm_addr = acpi_os_ioremap(comm_base_addr, len); if (!pcc_comm_addr) { @@ -604,7 +643,7 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps) (ref_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) || (nom_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) { /* Ring doorbell once to update PCC subspace */ - if (send_pcc_cmd(CMD_READ)) { + if (send_pcc_cmd(CMD_READ) < 0) { ret = -EIO; goto out_err; } @@ -662,7 +701,7 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs) 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)) { /* Ring doorbell once to update PCC subspace */ - if (send_pcc_cmd(CMD_READ)) { + if (send_pcc_cmd(CMD_READ) < 0) { ret = -EIO; goto out_err; } @@ -713,6 +752,13 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
spin_lock(&pcc_lock);
+ /* 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) { + ret = check_pcc_chan(); + if (ret) + goto busy_channel; + } + /* * Skip writing MIN/MAX until Linux knows how to come up with * useful values. @@ -722,10 +768,10 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls) /* 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)) + if (send_pcc_cmd(CMD_WRITE) < 0) ret = -EIO; } - +busy_channel: spin_unlock(&pcc_lock);
return ret;