Subject: [PATCHv3 1/2] hwrng: optee: handle unlimited data rates

Data rates of MAX_UINT32 will schedule an unnecessary one jiffy
timeout on the call to msleep. Avoid this scenario by using 0 as the
unlimited data rate.

Signed-off-by: Jorge Ramirez-Ortiz <[email protected]>
Reviewed-by: Sumit Garg <[email protected]>
---
drivers/char/hw_random/optee-rng.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
index 49b2e02537dd..5bc4700c4dae 100644
--- a/drivers/char/hw_random/optee-rng.c
+++ b/drivers/char/hw_random/optee-rng.c
@@ -128,7 +128,7 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
data += rng_size;
read += rng_size;

- if (wait) {
+ if (wait && pvt_data->data_rate) {
if (timeout-- == 0)
return read;
msleep((1000 * (max - read)) / pvt_data->data_rate);
--
2.17.1


Subject: [PATCHv3 2/2] hwrng: optee: fix wait use case

The current code waits for data to be available before attempting a
second read. However the second read would not be executed as the
while loop will exit.

This fix does not wait if all data has been read (skips the call to
msleep(0)) and reads a second time if partial data was retrieved on
the first read.

Worth noticing that since msleep(0) schedules a one jiffy timeout is
better to skip such a call.

Signed-off-by: Jorge Ramirez-Ortiz <[email protected]>
Reviewed-by: Sumit Garg <[email protected]>
---
drivers/char/hw_random/optee-rng.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
index 5bc4700c4dae..a99d82949981 100644
--- a/drivers/char/hw_random/optee-rng.c
+++ b/drivers/char/hw_random/optee-rng.c
@@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
if (max > MAX_ENTROPY_REQ_SZ)
max = MAX_ENTROPY_REQ_SZ;

- while (read == 0) {
+ while (read < max) {
rng_size = get_optee_rng_data(pvt_data, data, (max - read));

data += rng_size;
read += rng_size;

if (wait && pvt_data->data_rate) {
- if (timeout-- == 0)
+ if ((timeout-- == 0) || (read == max))
return read;
msleep((1000 * (max - read)) / pvt_data->data_rate);
} else {
--
2.17.1

2020-08-21 07:58:34

by Herbert Xu

[permalink] [raw]
Subject: Re: [PATCHv3 1/2] hwrng: optee: handle unlimited data rates

On Thu, Aug 06, 2020 at 12:00:09PM +0200, Jorge Ramirez-Ortiz wrote:
> Data rates of MAX_UINT32 will schedule an unnecessary one jiffy
> timeout on the call to msleep. Avoid this scenario by using 0 as the
> unlimited data rate.
>
> Signed-off-by: Jorge Ramirez-Ortiz <[email protected]>
> Reviewed-by: Sumit Garg <[email protected]>
> ---
> drivers/char/hw_random/optee-rng.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

All applied. Thanks.
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt