[media] dib7000p: avoid division by zero

dib7000p_read_word() may return zero on i2c errors, resulting in
dib7000p_get_internal_freq() returning zero.
So don't divide by the result of dib7000p_get_internal_freq()
without checking it for zero in dib7000p_set_dds().

On one of my machines the device
ID 2304:0229 Pinnacle Systems, Inc. PCTV Dual DVB-T 2001e
about once a day/every two days gets into a state, where
most (all?) I2C reads return with an error. Tuning during this
state will result in a divide by zero without this patch.
This patch doesn't fix the root cause for the device getting
into a bad state, but it allows me to unload/reload the drivers,
bringing it back into a usable state.

Signed-off-by: Martin Wache <M.Wache@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

diff --git a/drivers/media/dvb-frontends/dib7000p.c b/drivers/media/dvb-frontends/dib7000p.c
index a27c000..3815ea5 100644 (file)
--- a/drivers/media/dvb-frontends/dib7000p.c
+++ b/drivers/media/dvb-frontends/dib7000p.c
@@ -805,13 +805,19 @@ static int dib7000p_set_agc_config(struct dib7000p_state *state, u8 band)
        return 0;
 }
 
-static void dib7000p_set_dds(struct dib7000p_state *state, s32 offset_khz)
+static int dib7000p_set_dds(struct dib7000p_state *state, s32 offset_khz)
 {
        u32 internal = dib7000p_get_internal_freq(state);
-       s32 unit_khz_dds_val = 67108864 / (internal);   /* 2**26 / Fsampling is the unit 1KHz offset */
+       s32 unit_khz_dds_val;
        u32 abs_offset_khz = ABS(offset_khz);
        u32 dds = state->cfg.bw->ifreq & 0x1ffffff;
        u8 invert = !!(state->cfg.bw->ifreq & (1 << 25));
+       if (internal == 0) {
+               pr_warn("DIB7000P: dib7000p_get_internal_freq returned 0\n");
+               return -1;
+       }
+       /* 2**26 / Fsampling is the unit 1KHz offset */
+       unit_khz_dds_val = 67108864 / (internal);
 
        dprintk("setting a frequency offset of %dkHz internal freq = %d invert = %d\n", offset_khz, internal, invert);
 
@@ -828,6 +834,7 @@ static void dib7000p_set_dds(struct dib7000p_state *state, s32 offset_khz)
                dib7000p_write_word(state, 21, (u16) (((dds >> 16) & 0x1ff) | (0 << 10) | (invert << 9)));
                dib7000p_write_word(state, 22, (u16) (dds & 0xffff));
        }
+       return 0;
 }
 
 static int dib7000p_agc_startup(struct dvb_frontend *demod)
@@ -867,7 +874,9 @@ static int dib7000p_agc_startup(struct dvb_frontend *demod)
                        frequency_offset = (s32)frequency_tuner / 1000 - ch->frequency / 1000;
                }
 
-               dib7000p_set_dds(state, frequency_offset);
+               if (dib7000p_set_dds(state, frequency_offset) < 0)
+                       return -1;
+
                ret = 7;
                (*agc_state)++;
                break;