linux-kernel - RE: [PATCH] i2c: rcar: add SMBus block read support

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Date:   Thu, 18 Nov 2021 13:35:02 +0300
From:   Andrew Gabbasov <andrew_gabbasov@...tor.com>
To:     'Geert Uytterhoeven' <geert@...ux-m68k.org>
CC:     'Linux-Renesas' <linux-renesas-soc@...r.kernel.org>,
        'Linux I2C' <linux-i2c@...r.kernel.org>,
        'Linux Kernel Mailing List' <linux-kernel@...r.kernel.org>,
        'Wolfram Sang' <wsa+renesas@...g-engineering.com>,
        "Surachari, Bhuvanesh" <Bhuvanesh_Surachari@...tor.com>
Subject: RE: [PATCH] i2c: rcar: add SMBus block read support

Hello Geert, Wolfram,

Do you have any feedback on version 2 of this patch, that was submitted
after your review comments below?

https://lore.kernel.org/all/20211006182314.10585-1-andrew_gabbasov@mentor.com/

Thanks!

Best regards,
Andrew

> -----Original Message-----
> From: Andrew Gabbasov <andrew_gabbasov@...tor.com>
> Sent: Wednesday, October 06, 2021 9:12 PM
> To: 'Geert Uytterhoeven' <geert@...ux-m68k.org>
> Cc: Linux-Renesas <linux-renesas-soc@...r.kernel.org>; Linux I2C <linux-i2c@...r.kernel.org>; Linux Kernel
> Mailing List <linux-kernel@...r.kernel.org>; Wolfram Sang <wsa+renesas@...g-engineering.com>; Surachari,
> Bhuvanesh <Bhuvanesh_Surachari@...tor.com>
> Subject: RE: [PATCH] i2c: rcar: add SMBus block read support
> 
> Hi Geert,
> 
> Thank you for your review!
> 
> > -----Original Message-----
> > From: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Sent: Tuesday, October 05, 2021 4:32 PM
> > To: Gabbasov, Andrew <Andrew_Gabbasov@...tor.com>
> > Cc: Linux-Renesas <linux-renesas-soc@...r.kernel.org>; Linux I2C <linux-i2c@...r.kernel.org>; Linux Kernel
> > Mailing List <linux-kernel@...r.kernel.org>; Wolfram Sang <wsa+renesas@...g-engineering.com>; Surachari,
> > Bhuvanesh <Bhuvanesh_Surachari@...tor.com>
> > Subject: Re: [PATCH] i2c: rcar: add SMBus block read support
> >
> > Hi Andrew,
> >
> > On Wed, Sep 22, 2021 at 6:14 PM Andrew Gabbasov
> > <andrew_gabbasov@...tor.com> wrote:
> > > The smbus block read is not currently supported for rcar i2c devices.
> > > This patchset adds the support to rcar i2c bus so that blocks of data
> > > can be read using SMbus block reads.(using i2c_smbus_read_block_data()
> > > function from the i2c-core-smbus.c).
> > >
> > > Inspired by commit 8e8782c71595 ("i2c: imx: add SMBus block read support")
> > >
> > > This patch (adapted) was tested with v4.14, but due to lack of real
> > > hardware with SMBus block read operations support, using "simulation",
> > > that is manual analysis of data, read from plain I2C devices with
> > > SMBus block read request.
> > >
> > > Signed-off-by: Bhuvanesh Surachari <bhuvanesh_surachari@...tor.com>
> > > Signed-off-by: Andrew Gabbasov <andrew_gabbasov@...tor.com>
> >
> > Thanks for your patch!
> >
> > > --- a/drivers/i2c/busses/i2c-rcar.c
> > > +++ b/drivers/i2c/busses/i2c-rcar.c
> > > @@ -429,9 +431,16 @@ static bool rcar_i2c_dma(struct rcar_i2c_priv *priv)
> > >                 /*
> > >                  * The last two bytes needs to be fetched using PIO in
> > >                  * order for the STOP phase to work.
> > > +                *
> > > +                * For SMBus block read the first byte was received using PIO.
> >
> > So it might be easier to read, and more maintainable, to keep the
> > old assignments:
> >
> >     buf = priv->msg->buf;
> >     len = priv->msg->len - 2;
> >
> > and adjust them for SMBus afterwards:
> >
> >     if (block_data) {
> >             /* For SMBus block read the first byte was received using PIO */
> >             buf++;
> >             len--;
> >     }
> >
> > ?
> >
> > >                  */
> > > -               buf = priv->msg->buf;
> > > -               len = priv->msg->len - 2;
> > > +               if (block_data) {
> > > +                       buf = priv->msg->buf + 1;
> > > +                       len = priv->msg->len - 3;
> > > +               } else {
> > > +                       buf = priv->msg->buf;
> > > +                       len = priv->msg->len - 2;
> > > +               }
> > >         } else {
> > >                 /*
> > >                  * First byte in message was sent using PIO.
> >
> > And below we have another case handling buf and len :-(
> >
> > So perhaps:
> >
> >     buf = priv->msg->buf;
> >     len = priv->msg->len;
> >
> >     if (read) {
> >             /*
> >              * The last two bytes needs to be fetched using PIO in
> >              * order for the STOP phase to work.
> >              */
> >             len -= 2;
> >     }
> >     if (!read || block_data) {
> >             /* First byte in message was sent using PIO *
> >             buf++;
> >             len--;
> >     }
> 
> Probably I was trying to minimize the changes ;-)
> 
> However, I agree with you that the whole code fragment can be simplified
> and your variant indeed looks more clean and understandable.
> Thank you for your suggestion, I'll submit version 2 of the patch
> with this fragment changed.
> 
> Thanks!
> 
> Best regards,
> Andrew