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From: Miquel Raynal <miquel.raynal@bootlin.com>
To: James Hilliard <james.hilliard1@gmail.com>
Cc: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Jiri Slaby" <jirislaby@kernel.org>,
	"Raul E Rangel" <rrangel@chromium.org>,
	"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Heikki Krogerus" <heikki.krogerus@linux.intel.com>,
	"Phil Edworthy" <phil.edworthy@renesas.com>,
	linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH] serial: 8250: calculate TX length before preparing DMA flow control
Date: Fri, 23 Oct 2026 09:42:56 +0200	[thread overview]
Message-ID: <87cxt0q2v3.fsf@bootlin.com> (raw)
In-Reply-To: <20261022-submit-serial-8250-dma-tx-length-v1-v1-1-18cecc89a099@gmail.com> (James Hilliard's message of "Thu, 22 Oct 2026 11:14:41 -0600")

Hi James,

On 22/10/2026 at 11:14:41 -06, James Hilliard <james.hilliard1@gmail.com> wrote:

> The Renesas RZ/N1 preparation hook programs the UART DMA block size from
> dma->tx_size. The generic TX path calls that hook before calculating the
> length of the new transfer, so it programs zero on the first transfer and
> the previous length on subsequent transfers.
>
> Calculate the scatterlist length before calling the preparation hook so
> the UART flow controller and DMA descriptor use the same transfer size.
>
> Fixes: aa63d786cea2 ("serial: 8250: dw: Add support for DMA flow
> controlling devices")

This is the wrong fixes. Watch out 1788cf6a91d9 ("tty: serial: switch
from circ_buf to kfifo"). This is the one moving the size assignment
after the do_prepare_tx_dma() call.

Also requires to be backported, so Cc: stable.

Thanks,
Miquèl

      reply	other threads:[~2026-10-23  7:43 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-10-22 17:14 James Hilliard
2026-10-23  7:42 ` Miquel Raynal [this message]

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