linux-kernel - Re: [PATCH v3 3/3] i2c: smbus: switch from loops to memcpy

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Date:   Mon, 18 Nov 2019 09:47:17 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-iio@...r.kernel.org,
        Luca Ceresoli <luca@...aceresoli.net>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH v3 3/3] i2c: smbus: switch from loops to memcpy

On Mon, Nov 18, 2019 at 12:09:39AM -0800, Dmitry Torokhov wrote:
> On Mon, Nov 18, 2019 at 08:47:57AM +0100, Uwe Kleine-König wrote:
> > Hello Dmitry,
> > 
> > On Tue, Nov 12, 2019 at 12:31:32PM -0800, Dmitry Torokhov wrote:
> > > When copying memory from one buffer to another, instead of open-coding
> > > loops with byte-by-byte copies let's use memcpy() which might be a bit
> > > faster and makes intent more clear.
> > > 
> > > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > > 
> > > ---
> > > 
> > > Changes in v3:
> > > - new patch using memcpy() for moving data around
> > > 
> > >  drivers/i2c/i2c-core-smbus.c | 15 +++++----------
> > >  1 file changed, 5 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> > > index 7b4e2270eeda1..bbafdd3b1b114 100644
> > > --- a/drivers/i2c/i2c-core-smbus.c
> > > +++ b/drivers/i2c/i2c-core-smbus.c
> > > @@ -397,8 +397,7 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
> > >  			}
> > >  
> > >  			i2c_smbus_try_get_dmabuf(&msg[0], command);
> > > -			for (i = 1; i < msg[0].len; i++)
> > > -				msg[0].buf[i] = data->block[i - 1];
> > > +			memcpy(msg[0].buf + 1, data->block, msg[0].len - 1);
> > 
> > Can it happen that msg[0].len is zero?
> 
> No, it can not, because of the "msg[0].len = data->block[0] + 2;" line
> above.

OK, and as passing data with data->block[0] = 254 also makes the code do
strange things already without your patch. I now also checked the other
conversions for similar problems and didn't find any. So:

Acked-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
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