Message-ID: <5e144334-a747-7abf-4a8c-8f6f9134143b@ideasonboard.com>
Date:   Wed, 7 Feb 2018 23:30:43 +0000
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:     linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Jean-Michel Hautbois <jean-michel.hautbois@...alys.com>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        John Stultz <john.stultz@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Bhumika Goyal <bhumirks@...il.com>,
        Inki Dae <inki.dae@...sung.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm: adv7511: Add support for
 i2c_new_secondary_device

Hi Laurent,

On 07/02/18 21:59, Laurent Pinchart wrote:
> Hi Kieran,
> 
> On Wednesday, 7 February 2018 17:14:09 EET Kieran Bingham wrote:
>> On 29/01/18 10:26, Laurent Pinchart wrote:
>>> On Monday, 22 January 2018 14:50:00 EET Kieran Bingham wrote:
>>>> The ADV7511 has four 256-byte maps that can be accessed via the main I²C
>>>> ports. Each map has it own I²C address and acts as a standard slave
>>>> device on the I²C bus.
>>>>
>>>> Allow a device tree node to override the default addresses so that
>>>> address conflicts with other devices on the same bus may be resolved at
>>>> the board description level.
>>>>
>>>> Signed-off-by: Kieran Bingham <kieran.bingham@...asonboard.com>
>>>> ---
>>>>
>>>>  .../bindings/display/bridge/adi,adv7511.txt        | 10 +++++-
>>>
>>> I don't mind personally, but device tree maintainers usually ask for DT
>>> bindings changes to be split to a separate patch.
>>>
>>>>  drivers/gpu/drm/bridge/adv7511/adv7511.h           |  4 +++
>>>>  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c       | 36 ++++++++++-----
>>>>  3 files changed, 37 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git
>>>> a/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt
>>>> b/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt
>>>> index 0047b1394c70..f6bb9f6d3f48 100644
>>>> --- a/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt
>>>> +++ b/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt
>>>>
>>>> @@ -70,6 +70,9 @@ Optional properties:
>>>>    rather than generate its own timings for HDMI output.
>>>>  
>>>>  - clocks: from common clock binding: reference to the CEC clock.
>>>>  - clock-names: from common clock binding: must be "cec".
>>>>
>>>> +- reg-names : Names of maps with programmable addresses.
>>>> +	It can contain any map needing a non-default address.
>>>> +	Possible maps names are : "main", "edid", "cec", "packet"
>>>
>>> Is the reg-names property (and the additional maps) mandatory or optional
>>> ? If mandatory you should also update the existing DT sources that use
>>> those bindings.
>>
>> They are currently optional. I do prefer it that way - but perhaps due to an
>> issue mentioned below we might need to make this driver mandatory ?
>>
>>> If optional you should define which I2C addresses will be used when
>>> the maps are not specified (and in that case I think we should go for
>>> the addresses listed as default in the datasheet, which correspond to the
>>> current driver implementation when the main address is 0x3d/0x7a).
>>
>> The current addresses do not correspond to the datasheet, even when the
>> implementation main address is set to 0x3d.
> 
> Don't they ? The driver currently uses the following (8-bit) I2C addresses:
> 
> EDID:   main + 4  = 0x7e (0x3f)
> Packet: main - 10 = 0x70 (0x38)
> CEC:    main - 2  = 0x78 (0x3c)
> 
> Those are the default addresses according to section 4.1 of the ADV7511W 
> programming guide (rev. B), and they match the ones you set in this patch.

Sorry - I was clearly subtracting 8bit values from a 7bit address in my failed
assertion, to both you and Archit.



>> Thus, in my opinion - they are currently 'wrong' - but perhaps changing them
>> is considered breakage too.
>>
>> A particular issue will arise here too - as on this device - when the device
>> is in low-power mode (after probe, before use) - the maps will respond on
>> their *hardware default* addresses (the ones implemented in this patch),
>> and thus consume that address on the I2C bus regardless of their settings
>> in the driver.
> 
> We've discussed this previously and I share you concern. Just to make sure I 
> remember correctly, did all the secondary maps reset to their default 
> addresses, or just the EDID map ?


The following responds on the bus when programmed at alternative addresses, and
in low power mode. The responses are all 0, but that's still going to conflict
with other hardware if it tries to use the 'un-used' addresses.

Packet (0x38),
Main (0x39),
Fixed (set to 0 by software, but shows up at 0x3e)
and EDID (0x3f).

So actually it's only the CEC which don't respond when in "low-power-mode".


As far as I can see, (git grep  -B3 adi,adv75) - The r8a7792-wheat.dts is the
only instance of a device using 0x3d, which means that Sergei's patch changed
the behaviour of all the existing devices before that.

Thus - this patch could be seen to be a 'correction' back to the original
behaviour for all devices except the Wheat, and possibly devices added after
Sergei's patch went in.

However - by my understanding, - any device which has only one ADV75(3,1)+
should use the hardware defined addresses (the hardware defaults will be
conflicting on the bus anyway, thus should be assigned to the ADV7511)

Any platform which uses *two* ADV7511 devices on the same bus should actually
set *both* devices to use entirely separate addresses - or they will still
conflict with each other.

Now - if my understanding is correct - then I believe - that means that all
existing devices except Wheat *should* be using the default addresses as this
patch updates them to.

The Wheat - has an invalid configuration - and thus should be updated anyway.

Regards

Kieran

>>> You should also update the definition of the reg property that currently
>>> just states
>>>
>>> - reg: I2C slave address
>>>
>>> And finally you might want to define the term "map" in this context.
>>> Here's a proposal (if we make all maps mandatory).
>>>
>>> The ADV7511 internal registers are split into four pages exposed through
>>> different I2C addresses, creating four register maps. The I2C addresses of
>>> all four maps shall be specified by the reg and reg-names property.
>>>
>>> - reg: I2C slave addresses, one per reg-names entry
>>> - reg-names: map names, shall be "main", "edid", "cec", "packet"
>>>
>>>>  Required nodes:
>>>> @@ -88,7 +91,12 @@ Example
>>>>
>>>>  	adv7511w: hdmi@39 {
>>>>  		compatible = "adi,adv7511w";
>>>> -		reg = <39>;
>>>> +		/*
>>>> +		 * The EDID page will be accessible on address 0x66 on the i2c
>>>> +		 * bus. All other maps continue to use their default addresses.
>>>> +		 */
>>>> +		reg = <0x39 0x66>;
>>>> +		reg-names = "main", "edid";
>>>>  		interrupt-parent = <&gpio3>;
>>>>  		interrupts = <29 IRQ_TYPE_EDGE_FALLING>;
>>>>  		clocks = <&cec_clock>;
> 
> [snip]
> 
>>>> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>>> b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>>> index efa29db5fc2b..7ec33837752b 100644
>>>> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>>> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> 
> [snip]
> 
>>>> @@ -1153,24 +1151,35 @@ static int adv7511_probe(struct i2c_client *i2c,
>>>> const struct i2c_device_id *id)
>>>>  	if (ret)
>>>>  		goto uninit_regulators;
>>>>
>>>> -	regmap_write(adv7511->regmap, ADV7511_REG_EDID_I2C_ADDR,
>>>> edid_i2c_addr);
>>>> -	regmap_write(adv7511->regmap, ADV7511_REG_PACKET_I2C_ADDR,
>>>> -		     main_i2c_addr - 0xa);
>>>> -	regmap_write(adv7511->regmap, ADV7511_REG_CEC_I2C_ADDR,
>>>> -		     main_i2c_addr - 2);
>>>> -
>>>>  	adv7511_packet_disable(adv7511, 0xffff);
>>>> -	adv7511->i2c_edid = i2c_new_dummy(i2c->adapter, edid_i2c_addr >> 1);
>>>> +	adv7511->i2c_edid = i2c_new_secondary_device(i2c, "edid",
>>>> +					ADV7511_REG_EDID_I2C_ADDR_DEFAULT);
>>>>  	if (!adv7511->i2c_edid) {
>>>>  		ret = -ENOMEM;
>>>
>>> I wonder if this is the right error code. Maybe -EINVAL ? In most cases
>>> errors will be caused by invalid addresses (out of memory and
>>> device_register() failures can happen too but should be less common).
>>
>> It's arbitrary, as multiple error paths simply return NULL, but I think you
>> are right - the 'most common' fault here is likely to be an in use address.
>>
>> -ENOMEM was chosen here to mirror the equivalent code returned from the
>> adv7604 driver.
>>
>> Either way - -EINVAL does feel better at the moment. Although when mirrored
>> back to the ADV7604 that becomes a distinct change there.
>>
>> I don't think that matters though - so I'll apply this fix to both patches.
>>
>>> It would be nice if i2c_new_secondary_device() returned an ERR_PTR, but
>>> that's out of scope.
>>
>> I was about to say - well I'll add this, but the reality is it might require
>> updating all users of i2c_new_device, and i2c_new_dummy. Updating
>> i2c_new_secondary_device() on it's own seems a bit pointless otherwise.
>>
>> And that is definitely out of scope for the amount of time I currently have
>> :D
>>
>>>>  		goto uninit_regulators;
>>>>  	}
>>>>
>>>> +	regmap_write(adv7511->regmap, ADV7511_REG_EDID_I2C_ADDR,
>>>> +		     adv7511->i2c_edid->addr << 1);
>>>> +
>>>>  	ret = adv7511_init_cec_regmap(adv7511);
>>>>  	if (ret)
>>>>  		goto err_i2c_unregister_edid;
>>>>
>>>> +	regmap_write(adv7511->regmap, ADV7511_REG_CEC_I2C_ADDR,
>>>> +		     adv7511->i2c_cec->addr << 1);
>>>> +
>>>> +	adv7511->i2c_packet = i2c_new_secondary_device(i2c, "packet",
>>>> +					ADV7511_REG_PACKET_I2C_ADDR_DEFAULT);
>>>> +	if (!adv7511->i2c_packet) {
>>>> +		ret = -ENOMEM;
>>>> +		goto err_unregister_cec;
>>>> +	}
>>>> +
>>>> +	regmap_write(adv7511->regmap, ADV7511_REG_PACKET_I2C_ADDR,
>>>> +		     adv7511->i2c_packet->addr << 1);
>>>> +
>>>>  	INIT_WORK(&adv7511->hpd_work, adv7511_hpd_work);
>>>>  	
>>>>  	if (i2c->irq) {
> 
> [snip]
> 

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