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Subject: Re: [PATCH RESEND v8 2/4] input: elants: support old touch report
 format
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>
Cc:     Johnny Chuang <johnny.chuang.emc@gmail.com>,
        linux-input@vger.kernel.org, linux-kernel@vger.kernel.org
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Date:   Fri, 22 Jan 2021 23:10:52 +0300
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08.01.2021 01:06, Dmitry Osipenko пишет:
> 11.12.2020 21:48, Dmitry Torokhov пишет:
>> On Fri, Dec 11, 2020 at 06:04:01PM +0100, Michał Mirosław wrote:
>>> On Fri, Dec 11, 2020 at 07:39:33PM +0300, Dmitry Osipenko wrote:
>>>> 11.12.2020 19:09, Michał Mirosław пишет:
>>>>> On Thu, Dec 10, 2020 at 11:29:40PM -0800, Dmitry Torokhov wrote:
>>>>>> Hi Michał,
>>>>>> On Fri, Dec 11, 2020 at 07:53:56AM +0100, Michał Mirosław wrote:
>>>>>>> @@ -998,17 +1011,18 @@ static irqreturn_t elants_i2c_irq(int irq, void *_dev)
>>>>>>>  			}
>>>>>>>  
>>>>>>>  			report_len = ts->buf[FW_HDR_LENGTH] / report_count;
>>>>>>> -			if (report_len != PACKET_SIZE) {
>>>>>>> +			if (report_len != PACKET_SIZE &&
>>>>>>> +			    report_len != PACKET_SIZE_OLD) {
>>>>>>>  				dev_err(&client->dev,
>>>>>>> -					"mismatching report length: %*ph\n",
>>>>>>> +					"unsupported report length: %*ph\n",
>>>>>>>  					HEADER_SIZE, ts->buf);
>>>>>> Do I understand this correctly that the old packets are only observed on
>>>>>> EKTF3624? If so can we expand the check so that we only accept packets
>>>>>> with "old" size when we know we are dealing with this device?
>>>>>
>>>>> We only have EKTF3624 and can't be sure there are no other chips needing this.
>>>>
>>>> In practice this older packet format should be seen only on 3624, but
>>>> nevertheless we could make it more explicit by adding the extra chip_id
>>>> checks.
>>>>
>>>> It won't be difficult to change it in the future if will be needed.
>>>>
>>>> I think the main point that Dmitry Torokhov conveys here is that we
>>>> should minimize the possible impact on the current EKT3500 code since we
>>>> don't have definitive answers regarding the firmware differences among
>>>> the hardware variants.
>>>
>>> The only possible impact here is that older firmware instead of breaking
>>> would suddenly work. Maybe we can accept such a risk?
>>
>> These are not controllers we'll randomly find in devices: Windows boxes
>> use I2C HID, Chrome devices use "new" firmware, so that leaves random
>> ARM where someone needs to consciously add proper compatible before the
>> driver will engage with the controller.
>>
>> I would prefer we were conservative and not accept potentially invalid
>> data.
>>
>> Thanks.
>>
> 
> Michał, will you be able to make v9 with all the review comments addressed?
> 

I'll make a v9 over this weekend.

Michał, please let me know if you already started to work on this or
have any objections.