[2/3] hwrng: st: Report correct FIFO size

Message ID 1444142640-14721-2-git-send-email-lee.jones@linaro.org
State New
Headers show

Commit Message

Lee Jones Oct. 6, 2015, 2:43 p.m.
The values supplied to the 'read random data from FIFO' arithmetic
are not correct.  The value fed in to initialise the iterator
describes the FIFO depth, but then the iterator is treated in
Bytes and subsequently increased by 2 in value for every read
word.  This means only 4 of the 8 available values are being read
during each invocation of .read().

This change increased the device bandwidth by a factor of 2.

Reported-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
---
 drivers/char/hw_random/st-rng.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Lee Jones Oct. 6, 2015, 3:23 p.m. | #1
On Tue, 06 Oct 2015, Daniel Thompson wrote:

> On 06/10/15 15:43, Lee Jones wrote:
> >The values supplied to the 'read random data from FIFO' arithmetic
> >are not correct.  The value fed in to initialise the iterator
> >describes the FIFO depth, but then the iterator is treated in
> >Bytes and subsequently increased by 2 in value for every read
> >word.  This means only 4 of the 8 available values are being read
> >during each invocation of .read().
> >
> >This change increased the device bandwidth by a factor of 2.
> >
> >Reported-by: Daniel Thompson <daniel.thompson@linaro.org>
> >Signed-off-by: Lee Jones <lee.jones@linaro.org>
> >---
> >  drivers/char/hw_random/st-rng.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
> >index 8c8a435..44480fe 100644
> >--- a/drivers/char/hw_random/st-rng.c
> >+++ b/drivers/char/hw_random/st-rng.c
> >@@ -29,8 +29,9 @@
> >  #define ST_RNG_STATUS_BAD_ALTERNANCE	BIT(1)
> >  #define ST_RNG_STATUS_FIFO_FULL		BIT(5)
> >
> >-#define ST_RNG_FIFO_SIZE		8
> >  #define ST_RNG_SAMPLE_SIZE		2 /* 2 Byte (16bit) samples */
> >+#define ST_RNG_FIFO_DEPTH		8
> >+#define ST_RNG_FIFO_SIZE		(ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
> >
> >  /* Samples are available every 0.667us, which we round to 1us */
> >  #define ST_RNG_FILL_FIFO_TIMEOUT   (1 * (ST_RNG_FIFO_SIZE / ST_RNG_SAMPLE_SIZE))
> 
> This change doubles the timeout and doesn't mention it in the
> changelog.

The next patch renders this point moot.

> Changing the order of 2/3 and 3/3 would avoid this.

Right, if this is a real concern the patches can be applied in a
different order.

> Other than that:
> 
> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>

Thanking you.
Daniel Thompson Oct. 6, 2015, 3:48 p.m. | #2
On 06/10/15 15:43, Lee Jones wrote:
> The values supplied to the 'read random data from FIFO' arithmetic
> are not correct.  The value fed in to initialise the iterator
> describes the FIFO depth, but then the iterator is treated in
> Bytes and subsequently increased by 2 in value for every read
> word.  This means only 4 of the 8 available values are being read
> during each invocation of .read().
>
> This change increased the device bandwidth by a factor of 2.
>
> Reported-by: Daniel Thompson <daniel.thompson@linaro.org>
> Signed-off-by: Lee Jones <lee.jones@linaro.org>
> ---
>   drivers/char/hw_random/st-rng.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
> index 8c8a435..44480fe 100644
> --- a/drivers/char/hw_random/st-rng.c
> +++ b/drivers/char/hw_random/st-rng.c
> @@ -29,8 +29,9 @@
>   #define ST_RNG_STATUS_BAD_ALTERNANCE	BIT(1)
>   #define ST_RNG_STATUS_FIFO_FULL		BIT(5)
>
> -#define ST_RNG_FIFO_SIZE		8
>   #define ST_RNG_SAMPLE_SIZE		2 /* 2 Byte (16bit) samples */
> +#define ST_RNG_FIFO_DEPTH		8
> +#define ST_RNG_FIFO_SIZE		(ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
>
>   /* Samples are available every 0.667us, which we round to 1us */
>   #define ST_RNG_FILL_FIFO_TIMEOUT   (1 * (ST_RNG_FIFO_SIZE / ST_RNG_SAMPLE_SIZE))

This change doubles the timeout and doesn't mention it in the changelog. 
Changing the order of 2/3 and 3/3 would avoid this.

Other than that:

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.
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Patch

diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
index 8c8a435..44480fe 100644
--- a/drivers/char/hw_random/st-rng.c
+++ b/drivers/char/hw_random/st-rng.c
@@ -29,8 +29,9 @@ 
 #define ST_RNG_STATUS_BAD_ALTERNANCE	BIT(1)
 #define ST_RNG_STATUS_FIFO_FULL		BIT(5)
 
-#define ST_RNG_FIFO_SIZE		8
 #define ST_RNG_SAMPLE_SIZE		2 /* 2 Byte (16bit) samples */
+#define ST_RNG_FIFO_DEPTH		8
+#define ST_RNG_FIFO_SIZE		(ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
 
 /* Samples are available every 0.667us, which we round to 1us */
 #define ST_RNG_FILL_FIFO_TIMEOUT   (1 * (ST_RNG_FIFO_SIZE / ST_RNG_SAMPLE_SIZE))