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

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Date:   Mon, 20 Dec 2021 16:53:12 +0100
From:   Antonio Borneo <antonio.borneo@...s.st.com>
To:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Andrzej Hajda <a.hajda@...sung.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

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.

> > 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
> >