linux-kernel - Re: RFC: i2c designware gpio recovery

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Date:   Wed, 3 May 2017 09:30:50 +0800
From:   Phil Reid <preid@...ctromag.com.au>
To:     Tim Sander <tim@...eglstein.org>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: RFC: i2c designware gpio recovery

G'day Tim,

On 1/05/2017 21:31, Tim Sander wrote:
> Good Day Phil
> 
> Am Montag, 1. Mai 2017, 09:57:35 CEST schrieb Phil Reid:
>>> So i took a look into the device tree file socfpga.dtsi and found that the
>>> reset lines where not defined (although available in the corresponding
>>> reset manager). Is there a reason for this? Other components are
>>> connected.
>>
>> There's a few thing like that where the bootloader has been expected to
>> setup the resets etc.
> Yes, but if the resets are not connected in the device tree, the linux drivers
> are not going to use them?
Yes, so they should be added. I don't think we should assume the bootloader sets things up.
But that doesn't seem to have been the assumption with the Alter SOC's.

> 
>>> However with the patch below my previously sent patch works!
>>>
>>> If there is interest in would cleanup the patch and send it in for
>>> mainlining. I think the most unacceptable part would be this line:
>>> +       ret = gpio_request_one(bri->scl_gpio, //GPIOF_OPEN_DRAIN |
>>> My gpio drivers refuse to work as output as they have no open drain mode.
>>> So i wonder how to get this solved in a clean manner.
>>
>> I thought the gpio system would emulate open drain by switching the pin
>> between an input and output driven low in this case. How are you
>> configuring the GPIO's in the FPGA?
> I don't switch to GPIO mode. As the I2C logic is only pulling active low, i only do
> a wired and with the gpio (implemented in the fpga) port output on the output
> enable line for the SCL output.  SDA is only an additional input for the second in
> fpga gpio port.
> 
> A picture should make it a clearer:
> 
> gpio scl--\
> i2c   scl --&---i2c mode output pin (configured as fpga loan)
> 
> In my case the original i2c pins where occupied by some other logic conflicting
> so the i2c pins had to be shifted to some other pins using fpga logic. So it was
> just a matter of adding a two port gpio port.
I think I understand. What soft core gpio controller are you using?

> 
>> Given a couple of days I can test this on some flack i2c hardware I have
>> with a Cyclone-V SOC. I'm interested in the functionality as well.
> Sounds good. If you need some further input how i have configured the fpga
> drop me a line.
> 
>> For i2c that are connected to the dedicated HPS pins it should be possible
>> to reconfigure the pin mux controller (see system manager) in the HPS to
>> avoid the need to go thru the fpga to get direct control. The docs say this
>> is "unsupport" but I've done some test and it does seem to work.
> As far as i know the internal jtag chain is only used in the bootloader and there
> is no linux driver? But it shouldn't be a too big problem to port it to linux.
> 
> What i am unsure about is the fact that the internal jtag chain which controls the
> pinmuxing might wreak havoc on other pin states if you reconfigure it?

Have a look at the Cyclone V handbook "pin mux control Group REgister Descriptions"
 From what I can see the chain is used to configure IO standards and drive strength.
But not the actual muxes
> 
>> I'm guess
>> the no support is in a similar vain to the emac ptp FPGA interface couldn't
>> be used when the HPS pin where used. But that got changed when the user's
>> proved otherwise. There's just no pin ctrl driver yet to manage it.
> I am interested in this ptp solution too. Is there anything on the way to mainline?
> 

This was working the last time I tried it. I submitted a couple of minor patches for it a while ago.
My hardware has a DSA switch attached to the ethernet port and so far I haven't figured out how to
enable ptp when using the virtual lan ports on the DSA. But it worked fine when directly connected to
a phy.

-- 
Regards
Phil Reid