media: cxd2841er: avoid too many status inquires

I2C ops are expensive, as the I2C bus typical speed is 100kbps.

Also, stats reading take some time, as it requires to retrieve a
certain number of packets to complete.

While we don't know the minimal for CXD2841er, trying to do it
too quickly is still a very bad idea.

So, add some sanity logic there, preventing to retrieve stats
faster than one second.

This shouldn't cause any issues with well behavior apps, as they
usually take stats on a polling rate slower than 1 second.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sean Young <sean@mess.org>

diff --git a/drivers/media/dvb-frontends/cxd2841er.c b/drivers/media/dvb-frontends/cxd2841er.c
index 1b30cf570803a16326d1edc80ff2c318d7e5c422..758c95bc3b113e1ab27813941555d4518c054401 100644 (file)
--- a/drivers/media/dvb-frontends/cxd2841er.c
+++ b/drivers/media/dvb-frontends/cxd2841er.c
@@ -60,6 +60,7 @@ struct cxd2841er_priv {
        enum cxd2841er_xtal             xtal;
        enum fe_caps caps;
        u32                             flags;
+       unsigned long                   stats_time;
 };
 
 static const struct cxd2841er_cnr_data s_cn_data[] = {
@@ -3279,9 +3280,15 @@ static int cxd2841er_get_frontend(struct dvb_frontend *fe,
                p->strength.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
 
        if (status & FE_HAS_LOCK) {
+               if (priv->stats_time &&
+                   (!time_after(jiffies, priv->stats_time)))
+                       return 0;
+
+               /* Prevent retrieving stats faster than once per second */
+               priv->stats_time = jiffies + msecs_to_jiffies(1000);
+
                cxd2841er_read_snr(fe);
                cxd2841er_read_ucblocks(fe);
-
                cxd2841er_read_ber(fe);
        } else {
                p->cnr.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
@@ -3360,6 +3367,9 @@ done:
        p->post_bit_error.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
        p->post_bit_count.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
 
+       /* Reset the wait for jiffies logic */
+       priv->stats_time = 0;
+
        return ret;
 }