Re: [PATCH v10 43/55] dt-bindings: input: atmel: support to set max bytes transferred

[Wang, Jiada]

Hi Dmitry

On 2020/04/10 0:10, Dmitry Osipenko wrote:
> 09.04.2020 09:25, Wang, Jiada ÐÐÑÐÑ:
> > Hi Dmitry
> >
> > On 2020/04/07 23:47, Dmitry Osipenko wrote:
> > > 07.04.2020 12:27, Wang, Jiada ÐÐÑÐÑ:
> > > ..
> > > > > Is this a software (firmware) limitation which varies from version to
> > > > > version?
> > > >
> > > > the timeout issue trying to be addressed in this patch is from software,
> > > > one of our board a Serializer/Deserializer bridge exists between the SoC
> > > > (imx6) and the Atmel touch controller.
> > > > imx6 i2c controller driver has a timeout value(100ms) for each i2c
> > > > transaction,
> > > > Large i2c read transaction failed to complete within this timeout value
> > > > and therefore imx6 i2c controller driver aborts the transaction
> > > > and returns failure.
> > > >
> > > > Therefore this patch was created to split the large i2c transaction into
> > > > smaller chunks which can complete
> > > > within the timeout defined by i2c controller driver.
> > >
> > > Isn't it possible to use the max_read/write_len of the generic struct
> > > i2c_adapter_quirks for limiting the transfer size?
> > >
> > > BTW, it looks like the i.MX I2C driver doesn't specify the
> > > i2c_adapter_quirks, which probably needs to be fixed.
> > yes, i.MX I2C driver can specify i2c_adapter_quirks to limit the size be
> > transferred in one transaction.
> >
> > But even in this case, mxt_process_messages_t44() fails when it tries to
> > transfer data count larger than max_read/write_len set in i.MX I2C
> > driver, which we would like to avoid.
>
> IIUC, the transfer's limitation is a part of I2C controller hardware and
> not the touch controller, so it should be wrong to describe that
> limitation in the maxtouch's DT node.
>
> I meant that we probably could set the data->mtu based on
> i2c_client->adapter->quirks->max_read and then the DT property shouldn't
> be needed, couldn't this be done?
> Thanks, now I understand your point,
and yes, by this way, we can address the I2C controller limitation issue
by its own configuration.

I will replace this commit with your proposed solution

Thanks,
jiada


> The I2C core only rejects transfers that don't fit into the
> max_read/write_len and nothing more.