Re: [PATCH] i2c: mediatek: modify threshold passed to i2c_get_dma_safe_msg_buf()

Wolfram Sang
2019-02-15T16:37:02Z

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>> > Ok, I can add a check in another patch. Should we return NULL pointer
>> > if msg->len is 0 or print out some warnings? Thanks.
>>
>> No warning, msg->len == 0 is a valid setting. But interesting question:
>> I was about to say NULL, but your driver would assume ENOMEM there and
>> discard the message which is also not correct since msg->len == 0 is a
>> valid setting. So, should we just return msg->buf then? Will this work
>> with your driver? Can it handle zero-length transfers?
>
> dma_map_single(i2c->dev, msg->buf , msgs->len, DMA_TO_DEVICE); breaks
> kernel if msgs->len is 0, so I think it doesn't handle zero-length transfer.

Please don't drop the lists.

Then, the correct solution is to forbid those transfer with this
controller. Check I2C_AQ_NO_ZERO_LEN. Also, update the functionality
like this .. (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK).