Re: [PATCH] sc16is7xx: Fix for incorrect data being transmitted

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Feb 16, 2022 at 03:08:58PM +0000, Phil Elwell wrote:
> UART drivers are meant to use the port spinlock within certain
> methods, to protect against reentrancy. The sc16is7xx driver does
> very little locking, presumably because when added it triggers
> "scheduling while atomic" errors. This is due to the use of mutexes
> within the regmap abstraction layer, and the mutex implementation's
> habit of sleeping the current thread while waiting for access.
> Unfortunately this lack of interlocking can lead to corruption of
> outbound data, which occurs when the buffer used for I2C transmission
> is used simultaneously by two threads - a work queue thread running
> sc16is7xx_tx_proc, and an IRQ thread in sc16is7xx_port_irq, both
> of which can call sc16is7xx_handle_tx.
> 
> An earlier patch added efr_lock, a mutex that controls access to the
> EFR register. This mutex is already claimed in the IRQ handler, and
> all that is required is to claim the same mutex in sc16is7xx_tx_proc.
> 
> See: https://github.com/raspberrypi/linux/issues/4885
> 
> Signed-off-by: Phil Elwell <phil@raspberrypi.com>
> ---
>  drivers/tty/serial/sc16is7xx.c | 3 +++
>  1 file changed, 3 insertions(+)

What commit id does this fix?

thanks,

greg k-h