On 08/22/14 15:46, Laxman Dewangan wrote: > On Friday 22 August 2014 05:44 PM, Arnout Vandecappelle (Essensium/Mind) > wrote: > > From http://www.ti.com/lit/pdf/SWCZ010 : > > > > Glitch on SDA-SCL not managed correctly by the I2C IP > > > > Impact: > > The standard specifies that the I2C transfer should restart on a start > > event in all cases. The current design does not support two consecutive > > Start conditions. This can cause the first real access after such a > > glitch to be corrupted. > > > > Description: > > An unexpected glitch on SDA and SCL can generate a wrong start event. > > In the current design, the SCL line must toggle two times to detect a > > new start event and completely restart the I2C access; hence the real > > start event is not detected in the case of a single SCL toggle. > > > > Workaround: > > Repeat I2C access. > > > > The first access to the tps65910 that we do is when loading the regmap > > in the probe function. If there has been a glitch during boot and the > > erratum is triggered, then the regmap loading will fail with -REMOTEIO > > since the I2C transfer is not ACKed by the tps65910. > > > > A simple retry will work around it, because a subsequent I2C start > > condition is detected properly by the tps65910. > > > > Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arn...@mind.be> > > --- > > This patch is based on v3.17-rc1. > > Build-tested with omap2plus_defconfig. > > Runtime tested based on v3.4.97 with a custom config. > > --- > > drivers/mfd/tps65910.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/mfd/tps65910.c b/drivers/mfd/tps65910.c > > index f243e75..cc1ca33 100644 > > --- a/drivers/mfd/tps65910.c > > +++ b/drivers/mfd/tps65910.c > > @@ -487,8 +487,18 @@ static int tps65910_i2c_probe(struct i2c_client *i2c, > > tps65910->id = chip_id; > > > > I think one dummy read of any register unconditionally before regmap init will > resolve this issue. > Similar issue we face with Palmas TPS65913 and TI recommended to use dummy > read > before any valid transfer. >
Yeah, good idea. So something like i2c_master_send(i2c, "", 1); just before the regmap_init. Is abusing the empty string like that OK or should I declare a dummy buffer? Regards, Arnout -- Arnout Vandecappelle arnout at mind be Senior Embedded Software Architect +32-16-286500 Essensium/Mind http://www.mind.be G.Geenslaan 9, 3001 Leuven, Belgium BE 872 984 063 RPR Leuven LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle GPG fingerprint: 7CB5 E4CC 6C2E EFD4 6E3D A754 F963 ECAB 2450 2F1F -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
