| Message ID | 20230822152553.190858-1-martin@kaiser.cx |
|---|---|
| Headers | show |
| Series | hwrng: imx-rngc - use polling instead of interrupt | expand |
Am Dienstag, 22. August 2023, 17:25:51 CEST schrieb Martin Kaiser: > Use polling to detect the end of the rngc self test. This is much simpler > than using an interrupt and a completion. > > Active waiting is no disadvantage here. The self test is run during > probe, there's nothing we could do in parallel at this time. If this driver is built-in you are stalling the boot process while polling, no? Unless probe_type = PROBE_PREFER_ASYNCHRONOUS is set of course. Best regards, Alexander > Signed-off-by: Martin Kaiser <martin@kaiser.cx> > --- > drivers/char/hw_random/imx-rngc.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/drivers/char/hw_random/imx-rngc.c > b/drivers/char/hw_random/imx-rngc.c index e4b385b01b11..85207535fd12 100644 > --- a/drivers/char/hw_random/imx-rngc.c > +++ b/drivers/char/hw_random/imx-rngc.c > @@ -17,6 +17,7 @@ > #include <linux/hw_random.h> > #include <linux/completion.h> > #include <linux/io.h> > +#include <linux/iopoll.h> > #include <linux/bitfield.h> > > #define RNGC_VER_ID 0x0000 > @@ -101,21 +102,19 @@ static inline void imx_rngc_irq_unmask(struct imx_rngc > *rngc) > > static int imx_rngc_self_test(struct imx_rngc *rngc) > { > - u32 cmd; > + u32 cmd, status; > int ret; > > - imx_rngc_irq_unmask(rngc); > - > /* run self test */ > cmd = readl(rngc->base + RNGC_COMMAND); > writel(cmd | RNGC_CMD_SELF_TEST, rngc->base + RNGC_COMMAND); > > - ret = wait_for_completion_timeout(&rngc->rng_op_done, > msecs_to_jiffies(RNGC_TIMEOUT)); - imx_rngc_irq_mask_clear(rngc); > - if (!ret) > - return -ETIMEDOUT; > + ret = readl_poll_timeout(rngc->base + RNGC_STATUS, status, > + status & RNGC_STATUS_ST_DONE, 1000, RNGC_TIMEOUT * 1000); > + if (ret < 0) > + return ret; > > - return rngc->err_reg ? -EIO : 0; > + return readl(rngc->base + RNGC_ERROR) ? -EIO : 0; > } > > static int imx_rngc_read(struct hwrng *rng, void *data, size_t max, bool > wait)
Am Dienstag, 22. August 2023, 17:25:53 CEST schrieb Martin Kaiser: > Use polling to wait until the imx-rngc is properly seeded. What is the benefit of burning CPU cycles while waiting for hardware? > We do this only in the init function when the imx-rngc becomes active. > Polling is ok at this time, there's nothing else we could do while > we're waiting. > > We can now remove the code for the interrupt and the completion. Please split the change to polling and IRQ removal into two patches. > Signed-off-by: Martin Kaiser <martin@kaiser.cx> > --- > drivers/char/hw_random/imx-rngc.c | 81 ++++--------------------------- > 1 file changed, 9 insertions(+), 72 deletions(-) > > diff --git a/drivers/char/hw_random/imx-rngc.c > b/drivers/char/hw_random/imx-rngc.c index d2df468fd460..7ab9aada72d0 100644 > --- a/drivers/char/hw_random/imx-rngc.c > +++ b/drivers/char/hw_random/imx-rngc.c > @@ -63,12 +63,6 @@ struct imx_rngc { > struct clk *clk; > void __iomem *base; > struct hwrng rng; > - struct completion rng_op_done; > - /* > - * err_reg is written only by the irq handler and read only > - * when interrupts are masked, we need no spinlock > - */ > - u32 err_reg; > }; > > > @@ -91,15 +85,6 @@ static inline void imx_rngc_irq_mask_clear(struct > imx_rngc *rngc) writel(cmd, rngc->base + RNGC_COMMAND); > } > > -static inline void imx_rngc_irq_unmask(struct imx_rngc *rngc) > -{ > - u32 ctrl; > - > - ctrl = readl(rngc->base + RNGC_CONTROL); > - ctrl &= ~(RNGC_CTRL_MASK_DONE | RNGC_CTRL_MASK_ERROR); > - writel(ctrl, rngc->base + RNGC_CONTROL); > -} > - > static int imx_rngc_self_test(struct imx_rngc *rngc) > { > u32 cmd, status; > @@ -143,56 +128,32 @@ static int imx_rngc_read(struct hwrng *rng, void > *data, size_t max, bool wait) return retval ? retval : -EIO; > } > > -static irqreturn_t imx_rngc_irq(int irq, void *priv) > -{ > - struct imx_rngc *rngc = (struct imx_rngc *)priv; > - u32 status; > - > - /* > - * clearing the interrupt will also clear the error register > - * read error and status before clearing > - */ > - status = readl(rngc->base + RNGC_STATUS); > - rngc->err_reg = readl(rngc->base + RNGC_ERROR); > - > - imx_rngc_irq_mask_clear(rngc); > - > - if (status & (RNGC_STATUS_SEED_DONE | RNGC_STATUS_ST_DONE)) > - complete(&rngc->rng_op_done); > - > - return IRQ_HANDLED; > -} > - > static int imx_rngc_init(struct hwrng *rng) > { > struct imx_rngc *rngc = container_of(rng, struct imx_rngc, rng); > - u32 cmd, ctrl; > + u32 cmd, ctrl, status, err_reg; > int ret; > > /* clear error */ > cmd = readl(rngc->base + RNGC_COMMAND); > writel(cmd | RNGC_CMD_CLR_ERR, rngc->base + RNGC_COMMAND); > > - imx_rngc_irq_unmask(rngc); > - > /* create seed, repeat while there is some statistical error */ > do { > /* seed creation */ > cmd = readl(rngc->base + RNGC_COMMAND); > writel(cmd | RNGC_CMD_SEED, rngc->base + RNGC_COMMAND); > > - ret = wait_for_completion_timeout(&rngc->rng_op_done, > msecs_to_jiffies(RNGC_TIMEOUT)); - if (!ret) { > - ret = -ETIMEDOUT; > - goto err; > - } > + ret = readl_poll_timeout(rngc->base + RNGC_STATUS, status, > + status & RNGC_STATUS_SEED_DONE, 1000, RNGC_TIMEOUT * 1000); So you want to poll for up to 3s? Best regards, Alexander > + if (ret < 0) > + return ret; > > - } while (rngc->err_reg == RNGC_ERROR_STATUS_STAT_ERR); > + err_reg = readl(rngc->base + RNGC_ERROR); > + } while (err_reg == RNGC_ERROR_STATUS_STAT_ERR); > > - if (rngc->err_reg) { > - ret = -EIO; > - goto err; > - } > + if (err_reg) > + return -EIO; > > /* > * enable automatic seeding, the rngc creates a new seed automatically > @@ -202,23 +163,7 @@ static int imx_rngc_init(struct hwrng *rng) > ctrl |= RNGC_CTRL_AUTO_SEED; > writel(ctrl, rngc->base + RNGC_CONTROL); > > - /* > - * if initialisation was successful, we keep the interrupt > - * unmasked until imx_rngc_cleanup is called > - * we mask the interrupt ourselves if we return an error > - */ > return 0; > - > -err: > - imx_rngc_irq_mask_clear(rngc); > - return ret; > -} > - > -static void imx_rngc_cleanup(struct hwrng *rng) > -{ > - struct imx_rngc *rngc = container_of(rng, struct imx_rngc, rng); > - > - imx_rngc_irq_mask_clear(rngc); > } > > static int __init imx_rngc_probe(struct platform_device *pdev) > @@ -254,12 +199,9 @@ static int __init imx_rngc_probe(struct platform_device > *pdev) if (rng_type != RNGC_TYPE_RNGC && rng_type != RNGC_TYPE_RNGB) > return -ENODEV; > > - init_completion(&rngc->rng_op_done); > - > rngc->rng.name = pdev->name; > rngc->rng.init = imx_rngc_init; > rngc->rng.read = imx_rngc_read; > - rngc->rng.cleanup = imx_rngc_cleanup; > rngc->rng.quality = 19; > > rngc->dev = &pdev->dev; > @@ -267,11 +209,6 @@ static int __init imx_rngc_probe(struct platform_device > *pdev) > > imx_rngc_irq_mask_clear(rngc); > > - ret = devm_request_irq(&pdev->dev, > - irq, imx_rngc_irq, 0, pdev->name, (void *)rngc); > - if (ret) > - return dev_err_probe(&pdev->dev, ret, "Can't get interrupt working.\n"); > - > if (self_test) { > ret = imx_rngc_self_test(rngc); > if (ret)
Hi Alexander, thanks for reviewing the patches. Alexander Stein (alexander.stein@ew.tq-group.com) wrote: > Am Dienstag, 22. August 2023, 17:25:51 CEST schrieb Martin Kaiser: > > Use polling to detect the end of the rngc self test. This is much simpler > > than using an interrupt and a completion. > > Active waiting is no disadvantage here. The self test is run during > > probe, there's nothing we could do in parallel at this time. > If this driver is built-in you are stalling the boot process while > polling, no? According to the manual, "The self test takes approximately 29,000 cycles to complete." On my system, the rngb peripheral clock runs at 66.5MHz, i.e. the self test takes 436us. A poll interval of 480us and a timeout of 1.5ms are more appropriate than the current values (1ms poll interval, 3sec timeout). I'll fix this in v2. If it is unacceptable for a probe function to run for 1.5ms, we could probably move the self test to the init function. It's called when the rng is selected as the active rng. > Unless probe_type = PROBE_PREFER_ASYNCHRONOUS is set of > course. This does not work for drivers that use module_platform_driver_probe. We could switch to module_platform_driver. I'd prefer fixing the timing or moving the self test to init, though. Best regards, Martin
Hi Alexander, Alexander Stein (alexander.stein@ew.tq-group.com) wrote: > Am Dienstag, 22. August 2023, 17:25:53 CEST schrieb Martin Kaiser: > > Use polling to wait until the imx-rngc is properly seeded. > What is the benefit of burning CPU cycles while waiting for hardware? it seems to me that readl_poll_timeout readx_poll_timeout usleep_range usleep_range_state schedule_hrtimeout_range will not wait in the foreground and burn CPU cycles. The comment for schedule_hrtimeout_range says * Make the current task sleep until the given expiry time has * elapsed. > > We do this only in the init function when the imx-rngc becomes active. > > Polling is ok at this time, there's nothing else we could do while > > we're waiting. > > We can now remove the code for the interrupt and the completion. > Please split the change to polling and IRQ removal into two patches. Good point. Will do this in v2. > RNGC_STATUS_SEED_DONE, 1000, RNGC_TIMEOUT * 1000); > So you want to poll for up to 3s? According to the manual, "The initial seed takes approximately 2,000,000 clock cycles." With a 66.5MHz clock, this is approx 30ms. So that should be RNGC_STATUS_SEED_DONE, 20000, 100000); The comment for readx_poll_timeout suggests <= 20ms for the poll interval. Best regards, Martin