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

Dmitry Osipenko
2019-02-07T22:09:47Z

08.02.2019 0:47, Sowjanya Komatineni пишет:
> Tegra194 supports maximum 64K bytes transfer per packet.
> Tegra186 and prior supports maximum 4K bytes transfer per packet.
> This includes 12 bytes of packet header.
>
> This patch fixes max write length to account for packet header size
> for transfers.

The commit message isn't accurate. We are not actually fixing anything here, this patch is just a preparation for adding DMA support that require the packet-header size to be excluded from the overall TX size-quirk because the packet-header is the part of the DMA transfer.

Given how small this change is, it's probably not really worth to factor out it into a separate patch, let's just squash it to to the DMA-patch.

> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
> ---
> [V15] : This is new patch in this series.
>
> drivers/i2c/busses/i2c-tegra.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 3758c7a2c781..ab474cc86e0a 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -125,6 +125,9 @@
> #define I2C_MST_FIFO_STATUS_TX_MASK 0xff0000
> #define I2C_MST_FIFO_STATUS_TX_SHIFT 16
>
> +/* Packet header size in bytes */
> +#define I2C_PACKET_HEADER_SIZE 12
> +
> /*
> * msg_end_type: The bus control which need to be send at end of transfer.
> * @MSG_END_STOP: Send stop pulse at end of transfer.
> @@ -900,11 +903,13 @@ static const struct i2c_algorithm tegra_i2c_algo = {
> static const struct i2c_adapter_quirks tegra_i2c_quirks = {
> .flags = I2C_AQ_NO_ZERO_LEN,
> .max_read_len = 4096,
> - .max_write_len = 4096,
> + .max_write_len = 4096 - I2C_PACKET_HEADER_SIZE,
> };
>
> static const struct i2c_adapter_quirks tegra194_i2c_quirks = {
> .flags = I2C_AQ_NO_ZERO_LEN,
> + .max_read_len = 65535,
> + .max_write_len = 65535 - I2C_PACKET_HEADER_SIZE,
> };

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.