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

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Date:   Fri, 10 Apr 2020 15:53:38 +0900
From:   "Wang, Jiada" <jiada_wang@...tor.com>
To:     Dmitry Osipenko <digetx@...il.com>, <nick@...anahar.org>,
        <dmitry.torokhov@...il.com>, <jikos@...nel.org>,
        <benjamin.tissoires@...hat.com>, <bsz@...ihalf.com>
CC:     <linux-input@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <erosca@...adit-jv.com>, <Andrew_Gabbasov@...tor.com>,
        <Balasubramani_Vivekanandan@...tor.com>
Subject: Re: [PATCH v10 43/55] dt-bindings: input: atmel: support to set max
 bytes transferred

Hi Dmitry

On 2020/04/10 0:10, Dmitry Osipenko wrote:
> 09.04.2020 09:25, Wang, Jiada пишет:
>> Hi Dmitry
>>
>> On 2020/04/07 23:47, Dmitry Osipenko wrote:
>>> 07.04.2020 12:27, Wang, Jiada пишет:
>>> ..
>>>>> 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.
>