Re: [PATCH 1/3] hwrng: imx-rngc - use polling to detect end of self test

From: Alexander Stein <alexander.stein@ew.tq-group.com>
To: Herbert Xu <herbert@gondor.apana.org.au>,
	linux-arm-kernel@lists.infradead.org
Cc: linux-crypto@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, Martin Kaiser <martin@kaiser.cx>,
	Martin Kaiser <martin@kaiser.cx>
Subject: Re: [PATCH 1/3] hwrng: imx-rngc - use polling to detect end of self test
Date: Wed, 23 Aug 2023 07:23:32 +0200	[thread overview]
Message-ID: <3503619.mvXUDI8C0e@steina-w> (raw)
In-Reply-To: <20230822152553.190858-2-martin@kaiser.cx>

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)

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