| Message ID | 20230822152553.190858-4-martin@kaiser.cx (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | hwrng: imx-rngc - use polling instead of interrupt | expand |
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, 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
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); + 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)
Use polling to wait until the imx-rngc is properly seeded. 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. Signed-off-by: Martin Kaiser <martin@kaiser.cx> --- drivers/char/hw_random/imx-rngc.c | 81 ++++--------------------------- 1 file changed, 9 insertions(+), 72 deletions(-)