Hi Sakari, On Wed, Apr 18, 2018 at 01:41:54PM +0300, Sakari Ailus wrote: > On Wed, Apr 18, 2018 at 12:05:49PM +0200, jacopo mondi wrote: > > Hi Akinobu, > > > > On Mon, Apr 16, 2018 at 11:51:42AM +0900, Akinobu Mita wrote: > > > The ov772x driver only works when the i2c controller have > > > I2C_FUNC_PROTOCOL_MANGLING. However, many i2c controller drivers don't > > > support it. > > > > > > The reason that the ov772x requires I2C_FUNC_PROTOCOL_MANGLING is that > > > it doesn't support repeated starts. > > > > > > This changes the reading ov772x register method so that it doesn't > > > require I2C_FUNC_PROTOCOL_MANGLING by calling two separated i2c messages. > > > > > > Cc: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx> > > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > > > Cc: Hans Verkuil <hans.verkuil@xxxxxxxxx> > > > Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > > > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx> > > > Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx> > > > --- > > > * v2 > > > - Replace the implementation of ov772x_read() instead of adding an > > > alternative method > > > > I now wonder if my initial reply to this patch was wrong, and where > > possible we should try to use smbus operations... > > > > From Documentation/i2c/smbus-protocol > > "If you write a driver for some I2C device, please try to use the SMBus > > commands if at all possible... " and that's because, according to > > documentation, most I2c adapters support smbus protocol but may not > > support the full i2c command set. > > > > The fact this driver then restricts the supported adapters to the ones > > that support protocol mangling makes me think your change is fine, > > but as it often happens, I would scale this to more knowledgable > > people... > > Do you actually need to use this on SMBus adapters? A lot of sensor drivers > just use I²C; if SMBus support is really needed it can be always added back > later on... That was actually my question, sorry for not being clear. As the documentation says that SMBus has to be preferred when possible, I was wondering if ditching it completely in favour of plain I2c was wrong or not... I assume from your answer it is fine. > > -- > Sakari Ailus > e-mail: sakari.ailus@xxxxxx
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