Re: [PATCH 0/2] serial: keep the flushed TX buffer mapped until DMA has stopped

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

On Sat, Oct 31, 2026 at 12:37:47PM +0000, Samarth Narang wrote:
> This series addresses the DMA buffer lifetime issues in amba-pl011 and
> fsl_lpuart reported in the parent thread, where flush_buffer() unmaps
> the TX buffer before the terminated DMA transfer is guaranteed to have
> stopped accessing it. In fsl_lpuart, the buffer is unmapped even before
> termination is requested.
> 
> Since flush_buffer() runs under the port lock and cannot wait for DMA
> termination, both patches request termination while holding the lock and
> defer unmapping to a work item that first calls dmaengine_synchronize().
> The TX completion callback leaves the cleanup of flushed transfers to
> this work item, while shutdown, and suspend in the case of fsl_lpuart,
> waits for the work to finish before releasing the TX DMA state.
> 
> Both patches have only been compile-tested with arm64 defconfig, the
> relevant drivers enabled, and W=1, with no new warnings. I do not have
> access to PL011 or LPUART hardware with DMA support, so testing by
> someone with suitable hardware would be appreciated.
> 
> The imx driver also needs a fix for the issue reported in the same
> thread, but requires a different approach because its TX completion
> callback unmaps the scatterlist unconditionally. I will send that patch
> separately.

Again, these need to be tested on real hardware.  Not to mention the
bugs that sashiko just found in the changes as well.

thanks,

greg k-h