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Date:   Sat, 21 Nov 2020 10:47:31 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Joshua Thompson <funaho@...ai.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        stable <stable@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] m68k: Fix WARNING splat in pmac_zilog driver

On Fri, 20 Nov 2020, Geert Uytterhoeven wrote:

> Hi Finn,
> 
> On Fri, Nov 20, 2020 at 5:51 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> > Don't add platform resources that won't be used. This avoids a
> > recently-added warning from the driver core, that can show up on a
> > multi-platform kernel when !MACH_IS_MAC.
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 0 at drivers/base/platform.c:224 platform_get_irq_optional+0x8e/0xce
> > 0 is an invalid IRQ number
> > Modules linked in:
> > CPU: 0 PID: 0 Comm: swapper Not tainted 5.9.0-multi #1
> > Stack from 004b3f04:
> >         004b3f04 00462c2f 00462c2f 004b3f20 0002e128 004754db 004b6ad4 004b3f4c
> >         0002e19c 004754f7 000000e0 00285ba0 00000009 00000000 004b3f44 ffffffff
> >         004754db 004b3f64 004b3f74 00285ba0 004754f7 000000e0 00000009 004754db
> >         004fdf0c 005269e2 004fdf0c 00000000 004b3f88 00285cae 004b6964 00000000
> >         004fdf0c 004b3fac 0051cc68 004b6964 00000000 004b6964 00000200 00000000
> >         0051cc3e 0023c18a 004b3fc0 0051cd8a 004fdf0c 00000002 0052b43c 004b3fc8
> > Call Trace: [<0002e128>] __warn+0xa6/0xd6
> >  [<0002e19c>] warn_slowpath_fmt+0x44/0x76
> >  [<00285ba0>] platform_get_irq_optional+0x8e/0xce
> >  [<00285ba0>] platform_get_irq_optional+0x8e/0xce
> >  [<00285cae>] platform_get_irq+0x12/0x4c
> >  [<0051cc68>] pmz_init_port+0x2a/0xa6
> >  [<0051cc3e>] pmz_init_port+0x0/0xa6
> >  [<0023c18a>] strlen+0x0/0x22
> >  [<0051cd8a>] pmz_probe+0x34/0x88
> >  [<0051cde6>] pmz_console_init+0x8/0x28
> >  [<00511776>] console_init+0x1e/0x28
> >  [<0005a3bc>] printk+0x0/0x16
> >  [<0050a8a6>] start_kernel+0x368/0x4ce
> >  [<005094f8>] _sinittext+0x4f8/0xc48
> > random: get_random_bytes called from print_oops_end_marker+0x56/0x80 with crng_init=0
> > ---[ end trace 392d8e82eed68d6c ]---
> >
> > Cc: Michael Ellerman <mpe@...erman.id.au>
> > Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > Cc: Paul Mackerras <paulus@...ba.org>
> > Cc: Joshua Thompson <funaho@...ai.org>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Jiri Slaby <jirislaby@...nel.org>
> > Cc: stable@...r.kernel.org # v5.8+
> > References: commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> > Reported-by: Laurent Vivier <laurent@...ier.eu>
> > Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
> > ---
> > The global platform_device structs provide the equivalent of a direct
> > search of the OpenFirmware tree, for platforms that don't have OF.
> > The purpose of that search is discussed in the comments in pmac_zilog.c:
> >
> >          * First, we need to do a direct OF-based probe pass. We
> >          * do that because we want serial console up before the
> >          * macio stuffs calls us back
> >
> > The actual platform bus matching takes place later, with a module_initcall,
> > following the usual pattern.
> 
> I think it would be good for this explanation to be part of the
> actual patch description above.
> 

Thanks for your review.

I take that explanation as read because it was fundamental to the changes 
I made to pmac_zilog.c back in 2009 with commit ec9cbe09899e ("pmac-zilog: 
add platform driver").

IMO, being that it isn't news, it doesn't belong in the changelog. 
However, I agree that it needs to be documented. How about I add a comment 
to pmac_zilog.c?

> > --- a/arch/m68k/mac/config.c
> > +++ b/arch/m68k/mac/config.c
> > @@ -777,16 +777,12 @@ static struct resource scc_b_rsrcs[] = {
> >  struct platform_device scc_a_pdev = {
> >         .name           = "scc",
> >         .id             = 0,
> > -       .num_resources  = ARRAY_SIZE(scc_a_rsrcs),
> > -       .resource       = scc_a_rsrcs,
> >  };
> >  EXPORT_SYMBOL(scc_a_pdev);
> >
> >  struct platform_device scc_b_pdev = {
> >         .name           = "scc",
> >         .id             = 1,
> > -       .num_resources  = ARRAY_SIZE(scc_b_rsrcs),
> > -       .resource       = scc_b_rsrcs,
> >  };
> >  EXPORT_SYMBOL(scc_b_pdev);
> >
> > @@ -813,10 +809,15 @@ static void __init mac_identify(void)
> >
> >         /* Set up serial port resources for the console initcall. */
> >
> > -       scc_a_rsrcs[0].start = (resource_size_t) mac_bi_data.sccbase + 2;
> > -       scc_a_rsrcs[0].end   = scc_a_rsrcs[0].start;
> > -       scc_b_rsrcs[0].start = (resource_size_t) mac_bi_data.sccbase;
> > -       scc_b_rsrcs[0].end   = scc_b_rsrcs[0].start;
> > +       scc_a_rsrcs[0].start     = (resource_size_t)mac_bi_data.sccbase + 2;
> > +       scc_a_rsrcs[0].end       = scc_a_rsrcs[0].start;
> > +       scc_a_pdev.num_resources = ARRAY_SIZE(scc_a_rsrcs);
> > +       scc_a_pdev.resource      = scc_a_rsrcs;
> > +
> > +       scc_b_rsrcs[0].start     = (resource_size_t)mac_bi_data.sccbase;
> > +       scc_b_rsrcs[0].end       = scc_b_rsrcs[0].start;
> > +       scc_b_pdev.num_resources = ARRAY_SIZE(scc_b_rsrcs);
> > +       scc_b_pdev.resource      = scc_b_rsrcs;
> >
> >         switch (macintosh_config->scc_type) {
> >         case MAC_SCC_PSC:
> > diff --git a/drivers/tty/serial/pmac_zilog.c b/drivers/tty/serial/pmac_zilog.c
> > index 96e7aa479961..95abdb305d67 100644
> > --- a/drivers/tty/serial/pmac_zilog.c
> > +++ b/drivers/tty/serial/pmac_zilog.c
> > @@ -1697,18 +1697,17 @@ extern struct platform_device scc_a_pdev, scc_b_pdev;
> >
> >  static int __init pmz_init_port(struct uart_pmac_port *uap)
> >  {
> > -       struct resource *r_ports;
> > -       int irq;
> > +       struct resource *r_ports, *r_irq;
> >
> >         r_ports = platform_get_resource(uap->pdev, IORESOURCE_MEM, 0);
> > -       irq = platform_get_irq(uap->pdev, 0);
> > -       if (!r_ports || irq <= 0)
> > +       r_irq = platform_get_resource(uap->pdev, IORESOURCE_IRQ, 0);
> > +       if (!r_ports || !r_irq)
> >                 return -ENODEV;
> >
> >         uap->port.mapbase  = r_ports->start;
> >         uap->port.membase  = (unsigned char __iomem *) r_ports->start;
> >         uap->port.iotype   = UPIO_MEM;
> > -       uap->port.irq      = irq;
> > +       uap->port.irq      = r_irq->start;
> >         uap->port.uartclk  = ZS_CLOCK;
> >         uap->port.fifosize = 1;
> >         uap->port.ops      = &pmz_pops;
> 
> Given the resources are no longer present on !MAC, just doing
> 
>             r_ports = platform_get_resource(uap->pdev, IORESOURCE_MEM, 0);
>     +       if (!r_ports)
>     +               return -ENODEV;
>             irq = platform_get_irq(uap->pdev, 0);
> 
> should be sufficient?
> 

I think your suggestion is shorter but not better. Commit a85a6c86c25b 
(which introduced the WARNING) suggests that testing for irq == 0 is 
undesirable. My patch resolves that.

As a bonus, by simply testing for the existence of both resources, I've 
addressed the mistake I made when I originally added the slick 
platform_get_irq() call instead of consistently using 
platform_get_resource().

platform_get_irq() hides a bunch of architecture-specific logic that is 
not appropriate here. The WARNING itself is a good example of that kind of 
logic.

Do you agree? If so, I will add this explanation to the commit log.

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
> 

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