Re: [PATCH v1] i2c: tegra: Fix i2c_writesl() to use writel() instead of writesl()

[Sowjanya Komatineni]

On 1/12/21 1:32 AM, David Laight wrote:
> From: Sowjanya Komatineni
> > Sent: 11 January 2021 17:38
> ...
> > Using writesl() for filling TX_FIFO causing silent hang immediate on any
> > i2c register access after filling FIFO with 8 words and some times with
> > 6 words as well.
> >
> > So couldn't INTERRUPT_STATUS registers to check for TX FIFO Overflows
> > when this silent hang happens.
> >
> > Tried to read thru back-door (JTAG path) but could not connect to JTAG
> > either. Looks like Tegra chip is in some weird state.
> >
> > But using writel() followed by i2c_readl helps. Not sure if any thing
> > related to register access delay or some other issue.
> How much does the i2c_read() slow down the transfer?
> If the device is PCIe it is probably significant.
>
> If the underlying problem is that the Tegra chip can't handle
> back to back writes to the tx fifo maybe there are other solutions!
> 1) Send it back and ask for a working chip :-)
> 2) Maybe an interleaved write will slow things down enough?
>
> It may be worth testing back to back writes to other registers
> to see if it is a problem that is specific to the tx fifo.
>
> 	David
>
> -
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> Registration No: 1397386 (Wales)

This is a known hardware bug with VI I2C controller which is under 
host1x where immediate multiple writes to TX FIFO register gets stuck 
and reading from a register allows them to be flushed out.

VI I2C is dedicated for camera sensors or HDMI2CSI bridge.