linux-kernel - Re: [PATCH v2 07/15] drm/bridge: tc358767: Simplify AUX data write

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Date:   Fri, 22 Mar 2019 10:25:22 -0700
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     dri-devel@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrey Gusakov <andrey.gusakov@...entembedded.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 07/15] drm/bridge: tc358767: Simplify AUX data write

On Fri, Mar 22, 2019 at 3:51 AM Tomi Valkeinen <tomi.valkeinen@...com> wrote:
>
> On 22/03/2019 05:28, Andrey Smirnov wrote:
> > Simplify AUX data write by dropping index arithmetic and shifting and
> > replacing it with a call to a helper function that does three things:
> >
> >     1. Copies user-provided data into a write buffer
> >     2. Optionally fixes the endianness of the write buffer (not needed
> >        on LE hosts)
> >     3. Transfers contenst of the write buffer to up to 4 32-bit
> >        registers on the chip
> >
> > Note that separate data endianness fix:
> >
> >     tmp = (tmp << 8) | buf[i];
> >
> > that was reserved for DP_AUX_I2C_WRITE looks really strange, since it
> > will place data differently depending on the passed user-data
> > size. E.g. for a write of 1 byte, data transferred to the chip would
> > look like:
> >
> > [byte0] [dummy1] [dummy2] [dummy3]
> >
> > whereas for a write of 4 bytes we'd get:
> >
> > [byte3] [byte2] [byte1] [byte0]
> >
> > Since there's no indication in the datasheet that I2C write buffer
> > should be treated differently than AUX write buffer and no comment in
> > the original code explaining why it was done this way, that special
> > I2C write buffer transformation was dropped in this patch.
> >
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> > Cc: Archit Taneja <architt@...eaurora.org>
> > Cc: Andrzej Hajda <a.hajda@...sung.com>
> > Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> > Cc: Tomi Valkeinen <tomi.valkeinen@...com>
> > Cc: Andrey Gusakov <andrey.gusakov@...entembedded.com>
> > Cc: Philipp Zabel <p.zabel@...gutronix.de>
> > Cc: Chris Healy <cphealy@...il.com>
> > Cc: Lucas Stach <l.stach@...gutronix.de>
> > Cc: dri-devel@...ts.freedesktop.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> >  drivers/gpu/drm/bridge/tc358767.c | 58 +++++++++++++++++++------------
> >  1 file changed, 36 insertions(+), 22 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> > index 81c10a5d8106..21374565585d 100644
> > --- a/drivers/gpu/drm/bridge/tc358767.c
> > +++ b/drivers/gpu/drm/bridge/tc358767.c
> > @@ -307,6 +307,31 @@ static int tc_aux_get_status(struct tc_data *tc, u8 *reply)
> >       return 0;
> >  }
> >
> > +static int tc_aux_write_data(struct tc_data *tc, const void *data,
> > +                          size_t size)
> > +{
> > +     u32 auxwdata[DP_AUX_MAX_PAYLOAD_BYTES / sizeof(u32)] = { 0 };
> > +     int ret, i, count = DIV_ROUND_UP(size, 4);
>
> Should 4 there be sizeof(u32)?

Yup, will replace.

>
> > +
> > +     memcpy(auxwdata, data, size);
> > +
> > +     for (i = 0; i < count; i++) {
> > +             ret = regmap_write(tc->regmap, DP0_AUXWDATA(i),
> > +                                /*
> > +                                 * Our regmap is configured as LE
> > +                                 * for register data, so we need
> > +                                 * undo any byte swapping that will
> > +                                 * happened to preserve original
> > +                                 * byte order.
> > +                                 */
> > +                                cpu_to_le32(auxwdata[i]));
>
> Can regmap_bulk_write or regmap_raw_write be used here?
>

Not sure, will give it a try.

Thanks,
Andrey Smirnov