Re: [PATCH RESEND v8 2/4] input: elants: support old touch report format

From: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Johnny Chuang <johnny.chuang.emc@gmail.com>,
	linux-input@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND v8 2/4] input: elants: support old touch report format
Date: Fri, 22 Jan 2021 23:37:18 +0100	[thread overview]
Message-ID: <20210122223718.GE17048@qmqm.qmqm.pl> (raw)
In-Reply-To: <4c443c59-a7f8-bf16-cc0b-0e542c0d127f@gmail.com>

On Fri, Jan 22, 2021 at 11:10:52PM +0300, Dmitry Osipenko wrote:
> 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.

Hi,

Sorry for staying quiet so long. I have to revive my Transformer before
I can test anything, so please go ahead.

Best Regards
Michał Mirosław