linux-kernel - Re: [PATCH] serial: imx: disable DMA for RS-485 on i.MX6 SMP

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Date:   Tue, 20 Jun 2017 20:49:28 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Fugang Duan <fugang.duan@....com>
Subject: Re: [PATCH] serial: imx: disable DMA for RS-485 on i.MX6 SMP

Hi Clemens,

On Tue, Jun 20, 2017 at 1:13 PM, Fabio Estevam <festevam@...il.com> wrote:

> The subject gives the impression that the DMA will only be disabled
> for RS485, but the impact of this change is wider.
>
> For example: if I have a mx6q system with a Bluetooth serial
> connection I can no longer use DMA with your change applied.
>
> Ideally we should fix the RS485 DMA bug. If that is not possible, then
> at least we need to restrict this change to the RS485 case.
>
> Maybe we need to pass "linux,rs485-enabled-at-boot-time" in device
> tree and then use this property to deceide if DMA will be enabled or
> not:
>
> if (!uart_console(port) && !sport->dma_is_inited && !sport->rs485_enabled)

Could you please test the two attached patches and see if it solves the issue?

Unfortunately I no longer have access to the RS485 half-duplex board.

Just make sure to pass 'linux,rs485-enabled-at-boot-time' in your
device tree, thanks.

View attachment "0001-serial-imx-Allow-passing-linux-rs485-enabled-at-boot.patch" of type "text/x-patch" (1172 bytes)

View attachment "0002-serial-imx-Disable-DMA-for-RS485.patch" of type "text/x-patch" (2240 bytes)