Re: [PATCH v2 2/7] drm/i2c: tda998x: move CEC device initialisation later

[Russell King - ARM Linux <linux@armlinux.org.uk>]

On Tue, Dec 12, 2017 at 03:37:21PM +0100, Hans Verkuil wrote:
> Hi Russell,
> 
> On 08/12/17 12:59, Russell King - ARM Linux wrote:
> > On Wed, Dec 06, 2017 at 02:54:04PM +0100, Hans Verkuil wrote:
> >> On 12/06/17 13:35, Russell King wrote:
> >>> We no longer use the CEC client to access the CEC part itself, so we can
> >>> move this later in the initialisation sequence.
> >>>
> >>> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> >>> ---
> >>>  drivers/gpu/drm/i2c/tda998x_drv.c | 7 ++++---
> >>>  1 file changed, 4 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> index 7f4dbca7f7f4..4aeac2127974 100644
> >>> --- a/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> +++ b/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> @@ -1490,9 +1490,6 @@ static int tda998x_create(struct i2c_client *client, struct tda998x_priv *priv)
> >>>  	priv->cec_addr = 0x34 + (client->addr & 0x03);
> >>>  	priv->current_page = 0xff;
> >>>  	priv->hdmi = client;
> >>> -	priv->cec = i2c_new_dummy(client->adapter, priv->cec_addr);
> >>> -	if (!priv->cec)
> >>> -		return -ENODEV;
> >>>  
> >>>  	/* wake up the device: */
> >>>  	cec_write(priv, REG_CEC_ENAMODS,
> >>> @@ -1546,6 +1543,10 @@ static int tda998x_create(struct i2c_client *client, struct tda998x_priv *priv)
> >>>  			CEC_FRO_IM_CLK_CTRL_GHOST_DIS | CEC_FRO_IM_CLK_CTRL_IMCLK_SEL);
> >>>  
> >>>  	/* initialize the optional IRQ */
> >>> +	priv->cec = i2c_new_dummy(client->adapter, priv->cec_addr);
> >>> +	if (!priv->cec)
> >>> +		return -ENODEV;
> >>> +
> >>
> >> I'd move this up to before the 'initialize the optional IRQ' comment, since
> >> that should stay with the 'if (client->irq) {' line below.
> > 
> > I've swapped the order of patches 2 and 3, and moved this further down
> > near where we add the real cec device in a later patch.  This is
> > starting to get quite different from the patch series that I've tested,
> > and as I've already mentioned, testing is not going to happen for a
> > while.
> > 
> 
> I added support for this to am335x-boneblack-common.dtsi (see patch below), but
> it doesn't work. I suspect the calibration since I see these messages:
> 
> gpio-57 (nxp,calib): gpiod_direction_output: tried to set a GPIO tied to an IRQ as output

It's annoying that different gpiochips have different behaviours, it
means you can't develop a driver using gpios and know that it'll work
elsewhere.  It would be nice if everywhere behaved the same so that
could've been detected earlier.

> Which makes sense. I had a similar case in my cec-gpio driver and I had to completely
> free the interrupt before I could set the direction to output.
> 
> I do get nice interrupts when a transmit is done, so the interrupt works correctly.
> And it correctly detects Ack/Nack.
> 
> I looked a bit closer and I see that even without calibration the timings are reasonably
> OK: 2.3 ms for a bit period instead of the recommended 2.4 ms. Slightly off but within
> margins.
> 
> But receiving messages fails: I get no interrupt at all. Not sure if the lack of
> calibration is the cause of that, or if it is something else. I can take another look
> once the calibration is fixed.

Unfortuantely NXP don't document what the allowable tolerances are for
the chip.  I'd suggest getting the calibration working correctly would
be a good first step.

-- 
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