Re: [PATCH 2/3] i2c: xlr: fix extra read/write at end of rx transfer

From: Måns Rullgård
Date: Tue Dec 15 2015 - 07:48:18 EST

Wolfram Sang <wsa@xxxxxxxxxxxxx> writes:

> On Mon, Nov 02, 2015 at 02:03:37AM +0000, Mans Rullgard wrote:
>> The BYTECNT register holds the transfer size minus one. Setting it
>> to the correct value requires a dummy read/write only for zero-length
>> transfers as it is impossible to request one from the hardware. If a
>> zero-length transfer is requested, changing the length to 1 and setting
>> "buf" to a dummy location allows making the main loops less convoluted.
>> In other words, this patch makes the driver transfer the number of bytes
>> requested unless this is zero, which is not supported by the hardware,
>> in which case one byte is transferred instead.
> Uh, this is wrong, zero byte should really not transfer anything. We
> need to fix that and bail out, so probably something like
> if (!len)
> return -EOPNOTSUPP;

So the existing driver is wrong to allow it. Makes sense to drop that.

> Also, the xlr_func() should mask out I2C_FUNC_SMBUS_QUICK.


> Other than that, the patch looks good to me.
> Out of curiosity, your first driver had the registers 32bit apart. Now
> you can deal with 8bit. Is this configurable on this SoC?

It's all 32 bits. The XLR driver uses a u32 * to access the registers.

Måns Rullgård
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