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NFC: pn533: Add some polling entropy

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By not always starting the polling loop from the same modulation, we
avoid entering infinite loops where devices exporting 2 targets (on 2
different modulations) get the same target activated over and over.
If this target is not readable (e.g. a wallet emulating a tag), we will
stay in an error loop for ever.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
This commit is contained in:
Samuel Ortiz 2013-07-03 15:14:17 +02:00
parent 46f793b041
commit dfccd0f580
1 changed files with 6 additions and 1 deletions
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7
drivers/nfc/pn533.c
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@ -1913,6 +1913,7 @@ static int pn533_start_poll(struct nfc_dev *nfc_dev,
u32 im_protocols, u32 tm_protocols)
{
struct pn533 *dev = nfc_get_drvdata(nfc_dev);
u8 rand_mod;
nfc_dev_dbg(&dev->interface->dev,
"%s: im protocols 0x%x tm protocols 0x%x",
@ -1936,11 +1937,15 @@ static int pn533_start_poll(struct nfc_dev *nfc_dev,
tm_protocols = 0;
}
dev->poll_mod_curr = 0;
pn533_poll_create_mod_list(dev, im_protocols, tm_protocols);
dev->poll_protocols = im_protocols;
dev->listen_protocols = tm_protocols;
/* Do not always start polling from the same modulation */
get_random_bytes(&rand_mod, sizeof(rand_mod));
rand_mod %= dev->poll_mod_count;
dev->poll_mod_curr = rand_mod;
return pn533_send_poll_frame(dev);
}