RE: [PATCH V15 3/6] i2c: tegra: fix maximum transfer size

Sowjanya Komatineni
2019-02-08T15:25:45Z

> 08.02.2019 17:12, Peter Rosin пишет:
> > On 2019-02-08 13:46, Dmitry Osipenko wrote:
> >> 08.02.2019 1:25, Dmitry Osipenko пишет:
> >>>> 08.02.2019 1:16, Sowjanya Komatineni пишет:>
> >>>>>> This is wrong, 65535 = 64 * 1024 - 1.
> >>>>>>
> >>>>>> Let's just use size-constants provided by kernel:
> >>>>>>
> >>>>>> static const struct i2c_adapter_quirks tegra_i2c_quirks = {
> >>>>>> .flags = I2C_AQ_NO_ZERO_LEN,
> >>>>>> .max_read_len = SZ_4K,
> >>>>>> .max_write_len = SZ_4K - I2C_PACKET_HEADER_SIZE, };
> >>>>>>
> >>>>>> static const struct i2c_adapter_quirks tegra194_i2c_quirks = {
> >>>>>> .flags = I2C_AQ_NO_ZERO_LEN,
> >>>>>> .max_read_len = SZ_64K,
> >>>>>> .max_write_len = SZ_64K - I2C_PACKET_HEADER_SIZE, };
> >>>>>>
> >>>>>>
> >>>>>> I'll take a look at other patches later today, no need to send out new version right now.
> >>>>>>
> >>>>>>
> >>>>>
> >>>>> SIZE_64K is 0x00010000 (65536)
> >>>>>
> >>>>> msg len is u16 and max that can be set to msg.len is 65535
> >>>
> >>> Ah, okay. Then it looks about right, maybe it's time to change u16 to u32 in the I2C core.
> >>>
> >>
> >> Here is my suggestion:
> >>
> >> 1) Use SZ_4K / SZ_64K that I suggested above.
> >>
> >> 2) Squash this patch into the DMA-patch.
> >>
> >> 3) Add another patch (before the DMA-patch) that changes
> >> max_read_len/max_write_len types to u32 in the include/linux/i2c.h
> >
> > That is a bit naive and will not fly since the I2C core has a max
> > message size of 65535. Which is exposed to user space...
> >
> > Given the above, saying .max_read_len = 65535 a NOP (and is in fact
> > omitted in places where it would be needed if the type is changed). I
> > suggest that it is omitted here as well. But SZ_64K -
> > I2C_PACKET_HEADER_SIZE is still needed of course. At least if
> > I2C_PACKET_HEADER_SIZE is guaranteed to be non-zero?
>
> Ah, I missed that message len is also u16 and then we indeed could just drop the "max_read_len" for T194. Thank you Peter.
>
> Sowjanya, given the above, it probably better to define dma_buf max-size in the tegra_i2c_hw_feature.
>

I2C_PACKET_HEADER_SIZE is always fixed 12. So in that case, we can just add max_write_len
If no max_read_len, max will be 65535 anyway right

static const struct i2c_adapter_quirks tegra194_i2c_quirks = {
.flags = I2C_AQ_NO_ZERO_LEN,
.max_write_len = SZ_64K - I2C_PACKET_HEADER_SIZE, };

sowjanya