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SubjectRe: [PATCH 4/4] input: joystick: Fix buffer data parsing
Hi Jonathan,

Le ven., août 19 2022 at 18:53:39 +0100, Jonathan Cameron
<jic23@kernel.org> a écrit :
> On Wed, 17 Aug 2022 12:56:43 +0200
> Artur Rojek <contact@artur-rojek.eu> wrote:
>
>> Don't try to access buffer data of a channel by its scan index.
>> Instead,
>> use the newly introduced `iio_find_channel_offset_in_buffer` to get
>> the
>> correct data offset.
>>
>> The scan index of a channel does not represent its position in a
>> buffer,
>> as the buffer will contain data for enabled channels only, affecting
>> data offsets and alignment.
>>
>> Fixes: 2c2b364fddd5 ("Input: joystick - add ADC attached joystick
>> driver.")
>> Reported-by: Chris Morgan <macromorgan@hotmail.com>
>> Tested-by: Paul Cercueil <paul@crapouillou.net>
>> Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
>> ---
>> drivers/input/joystick/adc-joystick.c | 26
>> +++++++++++++++++---------
>> 1 file changed, 17 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/input/joystick/adc-joystick.c
>> b/drivers/input/joystick/adc-joystick.c
>> index c0deff5d4282..aed853ebe1d1 100644
>> --- a/drivers/input/joystick/adc-joystick.c
>> +++ b/drivers/input/joystick/adc-joystick.c
>> @@ -6,6 +6,7 @@
>> #include <linux/ctype.h>
>> #include <linux/input.h>
>> #include <linux/iio/iio.h>
>> +#include <linux/iio/buffer.h>
>> #include <linux/iio/consumer.h>
>> #include <linux/module.h>
>> #include <linux/platform_device.h>
>> @@ -46,36 +47,43 @@ static void adc_joystick_poll(struct input_dev
>> *input)
>> static int adc_joystick_handle(const void *data, void *private)
>> {
>> struct adc_joystick *joy = private;
>> + struct iio_buffer *buffer;
>> enum iio_endian endianness;
>> - int bytes, msb, val, idx, i;
>> - const u16 *data_u16;
>> + int bytes, msb, val, off;
>> + const u8 *chan_data;
>> + unsigned int i;
>> bool sign;
>>
>> bytes = joy->chans[0].channel->scan_type.storagebits >> 3;
>>
>> for (i = 0; i < joy->num_chans; ++i) {
>> - idx = joy->chans[i].channel->scan_index;
>> endianness = joy->chans[i].channel->scan_type.endianness;
>> msb = joy->chans[i].channel->scan_type.realbits - 1;
>> sign = tolower(joy->chans[i].channel->scan_type.sign) == 's';
>> + buffer = iio_channel_cb_get_iio_buffer(joy->buffer);
>> + off = iio_find_channel_offset_in_buffer(joy->chans[i].indio_dev,
>> + joy->chans[i].channel,
>> + buffer);
>
> With this call replaced with one that instead uses
>
> off = iio_find_channel_offset_in_buffer(joy->chans, i);
>
> which I'm fairly sure is enough via the info in chans[x]->channel to
> establish this offset.
>
> All is good, though you should probably cache it as doing that maths
> every
> time seems excessive.
>
>
>> + if (off < 0)
>> + return off;
>> +
>> + chan_data = (const u8 *)data + off;
>>
>> switch (bytes) {
>> case 1:
>> - val = ((const u8 *)data)[idx];
>> + val = *chan_data;
>> break;
>> case 2:
>> - data_u16 = (const u16 *)data + idx;
>> -
>> /*
>> * Data is aligned to the sample size by IIO core.
>> * Call `get_unaligned_xe16` to hide type casting.
>> */
>> if (endianness == IIO_BE)
>> - val = get_unaligned_be16(data_u16);
>> + val = get_unaligned_be16(chan_data);
>
> I obviously missed this previously but these are aligned so we don't
> need the
> unaligned form.

Yes, the comment above says that it's used to hide type casting.

Cheers,
-Paul

>> else if (endianness == IIO_LE)
>> - val = get_unaligned_le16(data_u16);
>> + val = get_unaligned_le16(chan_data);
>> else /* IIO_CPU */
>> - val = *data_u16;
>> + val = *(const u16 *)chan_data;
>> break;
>> default:
>> return -EINVAL;
>


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