[U-Boot] [PATCH 1/3] i2c: tegra: use repeated start for reads

[Stephen Warren]

On 06/25/2014 08:12 PM, Simon Glass wrote:
> Hi Stephen,
> 
> On 25 June 2014 10:57, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>
>> From: Stephen Warren <swarren at nvidia.com>
>>
>> I2C read transactions are typically implemented as follows:
>>
>> START(write) address REPEATED_START(read) data... STOP
>>
>> However, Tegra's I2C driver currently implements reads as follows:
>>
>> START(write) address STOP START(read) data... STOP
>>
>> This sequence confuses at least the AS3722 PMIC on the Jetson TK1 board,
>> leading to corrupted read data in some cases. Fix the driver to chain
>> the transactions together using repeated starts to solve this.

>> diff --git a/drivers/i2c/tegra_i2c.c b/drivers/i2c/tegra_i2c.c

>> @@ -209,7 +212,8 @@ static int send_recv_packets(struct i2c_bus *i2c_bus,
>>         int_status = readl(&control->int_status);
>>         writel(int_status, &control->int_status);
>>
>> -       send_packet_headers(i2c_bus, trans, 1);
>> +       send_packet_headers(i2c_bus, trans, 1,
>> +                           trans->flags & I2C_USE_REPEATED_START);
> 
> I'm not sure if it is safe/advisable to pass this value to a bool
> type. Perhaps the function parameter should be int? My understanding
> of bool is that it is supposed to be 0 or 1, but I'm happy to be
> corrected.

I believe that the "promotion" from int to bool clamps the range to 0 or
1. I've certainly seen compilers warn that this promotion might be a
performance issue!. If not, I can always add !! in front.