From: Andi Shyti <andi@etezian.org>
To: Stephan Gerhold <stephan@gerhold.net>
Cc: Andi Shyti <andi@etezian.org>,
Linux Input <linux-input@vger.kernel.org>,
Seung-Woo Kim <sw0312.kim@samsung.com>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Joonyoung Shim <jy0922.shim@samsung.com>
Subject: Re: [PATCH v2 1/2] Input: mms114 - use smbus functions whenever possible
Date: Mon, 21 Oct 2019 18:41:05 +0300 [thread overview]
Message-ID: <20191021154105.GC2278@jack.zhora.eu> (raw)
In-Reply-To: <20191021093423.GA1116@gerhold.net>
Hi Stephan,
> Not sure if you saw my comment regarding your patch [1],
> so I'll just repeat it properly inline here:
>
> [1]: https://patchwork.kernel.org/patch/11178515/#22927311
>
> On Sun, Oct 20, 2019 at 11:28:55PM +0300, Andi Shyti wrote:
> > The exchange of data to and from the mms114 touchscreen never
> > exceeds 256 bytes. In the worst case it goes up to 80 bytes in
> > the interrupt handler while reading the events.
> >
>
> i2c_smbus_read_i2c_block_data() is actually limited to
> I2C_SMBUS_BLOCK_MAX = 32.
oh sorry, I don't know how I slipped on this.
But this means that the i2c in the kernel is wrong (or outdated),
smbus specifies 256 bytes of data[*]. I might have relied on the
specification more than the code.
I guess SMBUS needs some update.
> > diff --git a/drivers/input/touchscreen/mms114.c b/drivers/input/touchscreen/mms114.c
> > index a5ab774da4cc..170dcb5312b9 100644
> > --- a/drivers/input/touchscreen/mms114.c
> > +++ b/drivers/input/touchscreen/mms114.c
> > @@ -204,14 +204,15 @@ static irqreturn_t mms114_interrupt(int irq, void *dev_id)
> > }
> > mutex_unlock(&input_dev->mutex);
> >
> > - packet_size = mms114_read_reg(data, MMS114_PACKET_SIZE);
> > + packet_size = i2c_smbus_read_byte_data(data->client,
> > + MMS114_PACKET_SIZE);
> > if (packet_size <= 0)
> > goto out;
> >
> > touch_size = packet_size / MMS114_PACKET_NUM;
> >
> > - error = __mms114_read_reg(data, MMS114_INFORMATION, packet_size,
> > - (u8 *)touch);
> > + error = i2c_smbus_read_i2c_block_data(data->client, MMS114_INFORMATION,
> > + packet_size, (u8 *)touch);
>
> ... and here we try to read up to 80 bytes, as you mentioned.
>
> i2c_smbus_read_i2c_block_data() will silently fall back to reading only
> 32 bytes. Therefore, if we try to read more than 32 bytes here we will
> later read uninitialized data.
>
> With this change, if you use more than 4 fingers you can easily trigger
> a situation where one of the fingers gets "stuck", together with:
> mms114 4-0048: Wrong touch type (0)
yes, it can be that for this there might be some delays or miss
reads.
> So we still need the custom functions here, or maybe avoid the problem
> by using regmap instead.
This was what Dmitry was proposing almost a couple of years ago,
but then I stopped working on this.
> > + error = i2c_smbus_read_i2c_block_data(data->client,
> > + MMS152_FW_REV, 3, buf);
> > if (error)
>
> i2c_smbus_read_i2c_block_data() returns the number of read bytes,
> therefore this check will always fail.
>
> It should be: if (error < 0)
> > + error = i2c_smbus_read_i2c_block_data(data->client,
> > + MMS114_TSP_REV, 6, buf);
> > if (error)
>
> As above.
Yes, an oversight in these two cases. Thanks!
Well, I guess some more rework needs to be done in this patch...
at the end Dmitry was right :)
Thanks,
Andi
[*] http://www.smbus.org/specs/
next prev parent reply other threads:[~2019-10-21 16:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-20 20:28 [PATCH v2 0/2] Use smbus functions to communicate through i2c Andi Shyti
2019-10-20 20:28 ` [PATCH v2 1/2] Input: mms114 - use smbus functions whenever possible Andi Shyti
2019-10-21 9:34 ` Stephan Gerhold
2019-10-21 15:41 ` Andi Shyti [this message]
2019-10-21 16:26 ` Stephan Gerhold
2019-10-21 16:39 ` Andi Shyti
2019-10-22 3:21 ` Dmitry Torokhov
2019-10-22 11:18 ` Andi Shyti
2019-11-18 13:32 ` Stephan Gerhold
2019-12-04 16:47 ` Stephan Gerhold
2019-10-20 20:28 ` [PATCH v2 2/2] Input: mms114 - get read of custm i2c read/write functions Andi Shyti
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