i3c_master_add_i3c_dev_locked() accept PID, BCR, DCR

vitor
2018-12-11T15:47:57Z

On 11/12/18 12:25, Boris Brezillon wrote:
> On Tue, 11 Dec 2018 13:21:03 +0100
> Boris Brezillon <bbrezillon@kernel.org> wrote:
>
>> On Tue, 11 Dec 2018 12:07:16 +0000
>> vitor <vitor.soares@synopsys.com> wrote:
>>
>>> On 11/12/18 11:58, Boris Brezillon wrote:
>>>>> I just want to skip GETBCR/DCR/PID operations since those data are
>>>>> already available in the controller. There's advantages but they
>>>>> only have relevance depending of use case.
>>>> Can you detail those use cases please?
>>> If the bus has a lot of devices and you want to decrease the
>>> initialization time this could be the first step.
>>>
>> Did you quantify the boot-time/perf improvement? The clk should be
>> running at 12.5MHz, GETPID takes 9bytes and GETBCR/DCR take 4 bytes
>> each. Let's add one byte per command to account for the start/stop
>> bits. That makes a total of 20bytes per device, with a maximum of 11
>> devices per bus:
>>
>> max_time_to_query_pid_bcr_dcr_per_bus = 20 * 10 / 12500000 = 17.6 usec.
> Sorry, small mistake, I counted bytes instead of bits.
>
> max_time_to_query_pid_bcr_dcr_per_bus = 20 * 8 * 11 / 12500000 = 141usec.

In fact there is missing other things like, S time, Sr time, stop time, stall time in t-bit and OD speed for the addresses...

I measured in my setup with a scope and the additional time to get that information is around 110 us per device and with only one device the bus takes around 550 us for the initialization.

>> Let's assume we have a huge overhead caused by the OS (and all the
>> scheduling involved), and make it 100usec.
> And let's make it 500usec with the OS overhead, which is still not
> particularly worrisome in term of boot-time.

Ok, it can be done in the future.

Thanks.