RE: [PATCH] tty: serial: sh-sci: Fix transmit end interrupt handler

From: Biju Das <biju.das.jz@bp.renesas.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	Stephen Boyd <swboyd@chromium.org>,
	"linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>,
	"linux-renesas-soc@vger.kernel.org" 
	<linux-renesas-soc@vger.kernel.org>,
	Linux-sh list <linux-sh@vger.kernel.org>
Subject: RE: [PATCH] tty: serial: sh-sci: Fix transmit end interrupt handler
Date: Fri, 17 Mar 2023 13:47:24 +0000	[thread overview]
Message-ID: <OS0PR01MB59220E5FA2CDC27108DB926C86BD9@OS0PR01MB5922.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <CAMuHMdW5jpnFBsHPbTE9QEbEYUNW9S0Qz93gg3QusLe0aSSbGg@mail.gmail.com>

Hi Geert,

Thanks for the feedback.

> Subject: Re: [PATCH] tty: serial: sh-sci: Fix transmit end interrupt handler
> 
> Hi Biju,
> 
> CC linux-sh
> 
> On Fri, Mar 17, 2023 at 10:15 AM Biju Das <biju.das.jz@bp.renesas.com>
> wrote:
> > > Subject: Re: [PATCH] tty: serial: sh-sci: Fix transmit end interrupt
> > > handler On Fri, Mar 17, 2023 at 9:08 AM Biju Das
> <biju.das.jz@bp.renesas.com> wrote:
> > > > > Subject: Re: [PATCH] tty: serial: sh-sci: Fix transmit end
> > > > > interrupt handler On Fri, Mar 17, 2023 at 8:59 AM Biju Das
> > > <biju.das.jz@bp.renesas.com> wrote:
> > > > > > > Subject: Re: [PATCH] tty: serial: sh-sci: Fix transmit end
> > > > > > > interrupt handler On Thu, Mar 16, 2023 at 5:34 PM Biju Das
> > > > > <biju.das.jz@bp.renesas.com> wrote:
> > > > > > > > > Subject: Re: [PATCH] tty: serial: sh-sci: Fix transmit
> > > > > > > > > end interrupt handler
> > > > > > >
> > > > > > > > > On Thu, Mar 16, 2023 at 5:01 PM Biju Das
> > > > > > > > > <biju.das.jz@bp.renesas.com>
> > > > > > > wrote:
> > > > > > > > > > The RZ SCI/ RZ/A1 SCIF has only 4 interrupts. The
> > > > > > > > > > fourth interrupt is transmit end interrupt, so shuffle
> > > > > > > > > > the interrupts to fix the transmit end interrupt
> > > > > > > > > > handler for these
> > > IPs.
> > > > > > > > > >
> > > > > > > > > > Fixes: 392fb8df528b ("serial: sh-sci: Use
> > > > > > > > > > platform_get_irq_optional() for optional interrupts")
> > > > > > > > >
> > > > > > > > > I don't think that's the right bad commit.
> > > > > > > >
> > > > > > > > OK. I will use below commit as fixes one, that is the
> > > > > > > > commit which added RZ/A1 SCIF with 4 interrupts.
> > > > > > > >
> > > > > > > > commit 8b0bbd956228ae87 ("serial: sh-sci: Add support for
> > > > > > > > R7S9210")
> > > > > > >
> > > > > > > That one added support for RZ/A2, and is also not the bad
> commit?
> > > > > >
> > > > > > OK will use below one,
> > > > > >
> > > > > > Fixes: 4c84c1b3acca ("ARM: shmobile: r7s72100: add scif nodes
> > > > > > to
> > > > > > dtsi")
> > > > >
> > > > > This really starts to look like a guessing game... Beep ;-)
> > > >
> > > > Already there is a generic compatible in driver, where we started
> > > > introducing RZ/A1 SoC With 4 interrupts. So addition of this SoC
> > > > has this
> > > issue. Am I missing anything here?
> > >
> > > The rabbit hole seems to be deeper than I thought...
> > >
> > > Looking at the code, the driver always assumed the fourth interrupt
> > > is BRI, which matches the RZ/A1 datasheet for SCIF.
> > > So the 4 IRQ case is really a subset of the 6 IRQ case, and
> > > Documentation/devicetree/bindings/serial/renesas,scif.yaml
> > > is wrong.
> >
> > OK.
> >
> > >
> > > However, SCI(g) is the odd one (also on SH): it has TEI as the
> > > fourth IRQ, which I probably missed when doing the json-schema
> > > conversion in commit 384d00fae8e51f8f ("dt-bindings: serial: sh-sci:
> > > Convert to json-schema"), leading to the bug in scif.yaml.
> > >
> > > Note that the driver never looks at the interrupt names, but uses
> > > indices exclusively.
> > >
> > > So I guess SCI has been broken on SH since forever, too?
> >
> > I think so, by looking at the changes done in tx to make it work on
> RZ/G2UL.
> > On RZ/G2UL both rx and tx is broken.
> >
> > Not sure SCI is tested ever on SH platform??
> >
> > Can any SH platform person confirm this?
> 
> SCI is only supported on
>   - sh770x,
>   - sh7750 (excluding rts7751r2d)
>     I know it's not exposed on my landisk,
>   - sh7760, for the SIM-port, which I doubt anyone uses.
> 
> FTR, I tried the "obvious" thing (remove the rts7751r2d-checks in
> arch/sh/kernel/cpu/sh4/setup-sh7750.c, and replace sci_br_interrupt as the
> interrupt handler by sci_tx_interrupt in sh-sci.c), but that didn't make
> ttySC0 work on qemu/rts7751r2d.

I am not seeing any SH platform SoCs in[1] and RZ/A2 does not have any SCI nodes
defined in dts, 

So Shall I use the below fixes tag instead, as it is documented in dt bindings and is the first
SoC with broken irq handler??

Fixes: f9a2adcc9e90 ("arm64: dts: renesas: r9a07g044: Add SCI[0-1] nodes")

With below check in driver.

+	/*
+	 * The fourth interrupt on SCI port is transmit end interrupt, so
+	 * shuffle the interrupts.
+	 */
+	if (p->type == PORT_SCI)
+		swap(sci_port->irqs[SCIx_BRI_IRQ], sci_port->irqs[SCIx_TEI_IRQ]);

[1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/devicetree/bindings/serial/renesas,sci.yaml?h=next-20230317

Cheers,
Biju