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From:   Andy Duan <fugang.duan@nxp.com>
To:     Vladimir Oltean <olteanv@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michael Walle <michael@walle.cc>
Subject: RE: [EXT] [PATCH] tty: serial: fsl_lpuart: LS1021A has a FIFO size of
 32 datawords
Thread-Topic: [EXT] [PATCH] tty: serial: fsl_lpuart: LS1021A has a FIFO size
 of 32 datawords
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Date:   Fri, 23 Oct 2020 01:44:45 +0000
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From: Vladimir Oltean <olteanv@gmail.com> Sent: Thursday, October 22, 2020 =
11:13 PM
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
>=20
> Similar to the workaround applied by Michael Walle in commit c2f448cff22a
> ("tty: serial: fsl_lpuart: add LS1028A support"), it turns out that the
> LPUARTx_FIFO encoding for fields TXFIFOSIZE and RXFIFOSIZE is the same fo=
r
> LS1028A as for LS1021A.
>=20
> The RXFIFOSIZE in the Layerscape SoCs is fixed at this value:
> 101 Receive FIFO/Buffer depth =3D 32 datawords.
>=20
> When Andy Duan wrote the commit in Fixes: below, he assumed that the 101
> encoding means 64 datawords. But this is not true for Layerscape. So that
> commit broke LS1021A, and this patch is extending the workaround for LS10=
28A
> which appeared in the meantime, to fix that breakage.
>=20
> When the driver thinks that it has a deeper FIFO than it really has, gett=
y (user
> space) output gets truncated.
>=20
> Many thanks to Michael for suggesting this!
>=20
> Fixes: f77ebb241ce0 ("tty: serial: fsl_lpuart: correct the FIFO depth siz=
e")
> Suggested-by: Michael Walle <michael@walle.cc>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Layerscape has different define for the FIFO size.

Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
> ---
>  drivers/tty/serial/fsl_lpuart.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>=20
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpu=
art.c index
> ff4b88c637d0..bd047e1f9bea 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -314,9 +314,10 @@ MODULE_DEVICE_TABLE(of, lpuart_dt_ids);
>  /* Forward declare this for the dma callbacks*/  static void
> lpuart_dma_tx_complete(void *arg);
>=20
> -static inline bool is_ls1028a_lpuart(struct lpuart_port *sport)
> +static inline bool is_layerscape_lpuart(struct lpuart_port *sport)
>  {
> -       return sport->devtype =3D=3D LS1028A_LPUART;
> +       return (sport->devtype =3D=3D LS1021A_LPUART ||
> +               sport->devtype =3D=3D LS1028A_LPUART);
>  }
>=20
>  static inline bool is_imx8qxp_lpuart(struct lpuart_port *sport) @@ -1701=
,11
> +1702,11 @@ static int lpuart32_startup(struct uart_port *port)
>=20
> UARTFIFO_FIFOSIZE_MASK);
>=20
>         /*
> -        * The LS1028A has a fixed length of 16 words. Although it suppor=
ts
> the
> -        * RX/TXSIZE fields their encoding is different. Eg the reference
> manual
> -        * states 0b101 is 16 words.
> +        * The LS1021A and LS1028A have a fixed FIFO depth of 16 words.
> +        * Although they support the RX/TXSIZE fields, their encoding is
> +        * different. Eg the reference manual states 0b101 is 16 words.
>          */
> -       if (is_ls1028a_lpuart(sport)) {
> +       if (is_layerscape_lpuart(sport)) {
>                 sport->rxfifo_size =3D 16;
>                 sport->txfifo_size =3D 16;
>                 sport->port.fifosize =3D sport->txfifo_size;
> --
> 2.25.1