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memory: tegra20-emc: Poll EMC-CaR handshake instead of waiting for interrupt

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The memory clock-rate change could be running on a non-boot CPU, while the
boot CPU handles the EMC interrupt. This introduces an unnecessary latency
since boot CPU should handle the interrupt and then notify the sibling CPU
about clock-rate change completion. In some rare cases boot CPU could be
in uninterruptible state for a significant time (like in a case of KASAN +
NFS root), it could get to the point that completion timeouts before boot
CPU gets a chance to handle interrupt. The solution is to get rid of the
completion and replace it with interrupt-status polling.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
This commit is contained in:
Dmitry Osipenko 2020-03-19 22:36:47 +03:00 • committed by Thierry Reding
parent 0553d7b204
commit adbcec8862
1 changed files with 11 additions and 17 deletions
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28
drivers/memory/tegra/tegra20-emc.c
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@ -7,11 +7,11 @@
#include <linux/clk.h> #include <linux/clk.h>
#include <linux/clk/tegra.h> #include <linux/clk/tegra.h>
#include <linux/completion.h>
#include <linux/debugfs.h> #include <linux/debugfs.h>
#include <linux/err.h> #include <linux/err.h>
#include <linux/interrupt.h> #include <linux/interrupt.h>
#include <linux/io.h> #include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/kernel.h> #include <linux/kernel.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/of.h> #include <linux/of.h>
@ -144,7 +144,6 @@ struct emc_timing {
struct tegra_emc { struct tegra_emc {
struct device *dev; struct device *dev;
struct completion clk_handshake_complete;
struct notifier_block clk_nb; struct notifier_block clk_nb;
struct clk *clk; struct clk *clk;
void __iomem *regs; void __iomem *regs;
@ -162,17 +161,13 @@ struct tegra_emc {
static irqreturn_t tegra_emc_isr(int irq, void *data) static irqreturn_t tegra_emc_isr(int irq, void *data)
{ {
struct tegra_emc *emc = data; struct tegra_emc *emc = data;
u32 intmask = EMC_REFRESH_OVERFLOW_INT | EMC_CLKCHANGE_COMPLETE_INT; u32 intmask = EMC_REFRESH_OVERFLOW_INT;
u32 status; u32 status;
status = readl_relaxed(emc->regs + EMC_INTSTATUS) & intmask; status = readl_relaxed(emc->regs + EMC_INTSTATUS) & intmask;
if (!status) if (!status)
return IRQ_NONE; return IRQ_NONE;
/* notify about EMC-CAR handshake completion */
if (status & EMC_CLKCHANGE_COMPLETE_INT)
complete(&emc->clk_handshake_complete);
/* notify about HW problem */ /* notify about HW problem */
if (status & EMC_REFRESH_OVERFLOW_INT) if (status & EMC_REFRESH_OVERFLOW_INT)
dev_err_ratelimited(emc->dev, dev_err_ratelimited(emc->dev,
@ -224,14 +219,13 @@ static int emc_prepare_timing_change(struct tegra_emc *emc, unsigned long rate)
/* wait until programming has settled */ /* wait until programming has settled */
readl_relaxed(emc->regs + emc_timing_registers[i - 1]); readl_relaxed(emc->regs + emc_timing_registers[i - 1]);
reinit_completion(&emc->clk_handshake_complete);
return 0; return 0;
} }
static int emc_complete_timing_change(struct tegra_emc *emc, bool flush) static int emc_complete_timing_change(struct tegra_emc *emc, bool flush)
{ {
unsigned long timeout; int err;
u32 v;
dev_dbg(emc->dev, "%s: flush %d\n", __func__, flush); dev_dbg(emc->dev, "%s: flush %d\n", __func__, flush);
@ -242,11 +236,12 @@ static int emc_complete_timing_change(struct tegra_emc *emc, bool flush)
return 0; return 0;
} }
timeout = wait_for_completion_timeout(&emc->clk_handshake_complete, err = readl_relaxed_poll_timeout_atomic(emc->regs + EMC_INTSTATUS, v,
msecs_to_jiffies(100)); v & EMC_CLKCHANGE_COMPLETE_INT,
if (timeout == 0) { 1, 100);
dev_err(emc->dev, "EMC-CAR handshake failed\n"); if (err) {
return -EIO; dev_err(emc->dev, "emc-car handshake timeout: %d\n", err);
return err;
} }
return 0; return 0;
@ -412,7 +407,7 @@ tegra_emc_find_node_by_ram_code(struct device *dev)
static int emc_setup_hw(struct tegra_emc *emc) static int emc_setup_hw(struct tegra_emc *emc)
{ {
u32 intmask = EMC_REFRESH_OVERFLOW_INT | EMC_CLKCHANGE_COMPLETE_INT; u32 intmask = EMC_REFRESH_OVERFLOW_INT;
u32 emc_cfg, emc_dbg; u32 emc_cfg, emc_dbg;
emc_cfg = readl_relaxed(emc->regs + EMC_CFG_2); emc_cfg = readl_relaxed(emc->regs + EMC_CFG_2);
@ -686,7 +681,6 @@ static int tegra_emc_probe(struct platform_device *pdev)
return -ENOMEM; return -ENOMEM;
} }
init_completion(&emc->clk_handshake_complete);
emc->clk_nb.notifier_call = tegra_emc_clk_change_notify; emc->clk_nb.notifier_call = tegra_emc_clk_change_notify;
emc->dev = &pdev->dev; emc->dev = &pdev->dev;