linux-kernel - Re: [PATCH] drm: adv7511: override i2c address of cec before accessing it

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Message-ID: <164008679146.2512616.5965783147922289011@Monstersaurus>
Date:   Tue, 21 Dec 2021 11:39:51 +0000
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Antonio Borneo <antonio.borneo@...s.st.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH] drm: adv7511: override i2c address of cec before accessing it

Quoting Antonio Borneo (2021-12-20 15:53:12)
> On Mon, 2021-12-20 at 14:54 +0000, Kieran Bingham wrote:
> > Hi Antonio,
> > 
> > Quoting Antonio Borneo (2021-12-18 18:28:04)
> > > Commit 680532c50bca ("drm: adv7511: Add support for
> > > i2c_new_secondary_device") allows a device tree node to override
> > > the default addresses of the secondary i2c devices. This is useful
> > > for solving address conflicts on the i2c bus.
> > > 
> > > In adv7511_init_cec_regmap() the new i2c address of cec device is
> > > read from device tree and immediately accessed, well before it is
> > > written in the proper register to override the default address.
> > > This can cause an i2c error during probe and a consequent probe
> > > failure.
> > 
> > Ouch, it does seem that way. I guess no one has used the CEC for
> > quite
> > some time, as it must have been like this for a while?
> 
> Using the default i2c address for cec works without problem; apparently
> everyone is happy with such default. The issue appears only when you
> have to override the default cec address.
> The commit 680532c50bca landed in v4.18.

Ok, phew - so the 'normal' case still worked. That makes sense.

Sorry for getting it wrong, and I hope it didn't take too long to find
and fix. I'm sure we'll see it percolate down the stable trees once
integrated.

--
Kieran

> > > Once the new i2c address is read from the device tree, override
> > > the default address before any attempt to access the cec.
> > 
> > Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> 
> Thanks!
> Antonio
> 
> > > Tested with adv7533 and stm32mp157f.
> > > 
> > > Signed-off-by: Antonio Borneo <antonio.borneo@...s.st.com>
> > > Fixes: 680532c50bca ("drm: adv7511: Add support for
> > > i2c_new_secondary_device")
> > > ---
> > > To: Andrzej Hajda <a.hajda@...sung.com>
> > > To: Neil Armstrong <narmstrong@...libre.com>
> > > To: Robert Foss <robert.foss@...aro.org>
> > > To: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> > > To: Jonas Karlman <jonas@...boo.se>
> > > To: Jernej Skrabec <jernej.skrabec@...il.com>
> > > To: David Airlie <airlied@...ux.ie>
> > > To: Daniel Vetter <daniel@...ll.ch>
> > > To: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> > > To: dri-devel@...ts.freedesktop.org
> > > Cc: linux-kernel@...r.kernel.org
> > > Cc: linux-stm32@...md-mailman.stormreply.com
> > > ---
> > >  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > index 76555ae64e9c..629e05286fd9 100644
> > > --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > @@ -1048,6 +1048,10 @@ static int adv7511_init_cec_regmap(struct
> > > adv7511 *adv)
> > >                                                
> > > ADV7511_CEC_I2C_ADDR_DEFAULT);
> > >         if (IS_ERR(adv->i2c_cec))
> > >                 return PTR_ERR(adv->i2c_cec);
> > > +
> > > +       regmap_write(adv->regmap, ADV7511_REG_CEC_I2C_ADDR,
> > > +                    adv->i2c_cec->addr << 1);
> > > +
> > >         i2c_set_clientdata(adv->i2c_cec, adv);
> > >  
> > >         adv->regmap_cec = devm_regmap_init_i2c(adv->i2c_cec,
> > > @@ -1252,9 +1256,6 @@ static int adv7511_probe(struct i2c_client
> > > *i2c, const struct i2c_device_id *id)
> > >         if (ret)
> > >                 goto err_i2c_unregister_packet;
> > >  
> > > -       regmap_write(adv7511->regmap, ADV7511_REG_CEC_I2C_ADDR,
> > > -                    adv7511->i2c_cec->addr << 1);
> > > -
> > >         INIT_WORK(&adv7511->hpd_work, adv7511_hpd_work);
> > >  
> > >         if (i2c->irq) {
> > > 
> > > base-commit: fc74881c28d314b10efac016ef49df4ff40b8b97
> > > -- 
> > > 2.34.1
> > > 
>