Re: [PATCH V5 6/7] i2c: tegra: fix PIO rx/tx residual transfer check

From: Bitan Biswas
Date: Thu Jun 13 2019 - 11:33:12 EST

On 6/12/19 7:30 AM, Dmitry Osipenko wrote:
11.06.2019 13:51, Bitan Biswas ÐÐÑÐÑ:
Fix expression for residual bytes(less than word) transfer
in I2C PIO mode RX/TX.

Signed-off-by: Bitan Biswas <bbiswas@xxxxxxxxxx>


- * Update state before writing to FIFO. If this casues us
+ * Update state before writing to FIFO. If this causes us
* to finish writing all bytes (AKA buf_remaining goes to 0) we
* have a potential for an interrupt (PACKET_XFER_COMPLETE is
- * not maskable). We need to make sure that the isr sees
- * buf_remaining as 0 and doesn't call us back re-entrantly.
+ * not maskable).
buf_remaining -= words_to_transfer * BYTES_PER_FIFO_WORD;

Looks like the comment could be removed altogether because it doesn't
make sense since interrupt handler is under xfer_lock which is kept
locked during of tegra_i2c_xfer_msg().
I would push a separate patch to remove this comment because of xfer_lock in ISR now.

Moreover the comment says that "PACKET_XFER_COMPLETE is not maskable",
but then what I2C_INT_PACKET_XFER_COMPLETE masking does?

I2C_INT_PACKET_XFER_COMPLETE masking support available in Tegra chips newer than Tegra30 allows one to not see interrupt after Packet transfer complete. With the xfer_lock in ISR the scenario discussed in comment can be ignored.