[PATCH] m68k: Fix WARNING splat in pmac_zilog driver

[PATCH] m68k: Fix WARNING splat in pmac_zilog driver

[Finn Thain]

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@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Joshua Thompson <funaho@jurai.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: stable@vger.kernel.org # v5.8+
References: commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
Reported-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Finn Thain <fthain@telegraphics.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.
---
 arch/m68k/mac/config.c          | 17 +++++++++--------
 drivers/tty/serial/pmac_zilog.c |  9 ++++-----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/m68k/mac/config.c b/arch/m68k/mac/config.c
index 0ac53d87493c..2bea1799b8de 100644
--- 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;
-- 
2.26.2

Re: [PATCH] m68k: Fix WARNING splat in pmac_zilog driver

[Geert Uytterhoeven]

Hi Finn,

On Fri, Nov 20, 2020 at 5:51 AM Finn Thain <fthain@telegraphics.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@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Joshua Thompson <funaho@jurai.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jiri Slaby <jirislaby@kernel.org>
> Cc: stable@vger.kernel.org # v5.8+
> References: commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> Reported-by: Laurent Vivier <laurent@vivier.eu>
> Signed-off-by: Finn Thain <fthain@telegraphics.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.

> --- 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?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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

Re: [PATCH] m68k: Fix WARNING splat in pmac_zilog driver

[Finn Thain]

On Fri, 20 Nov 2020, Geert Uytterhoeven wrote:

> Hi Finn,
> 
> On Fri, Nov 20, 2020 at 5:51 AM Finn Thain <fthain@telegraphics.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@ellerman.id.au>
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Paul Mackerras <paulus@samba.org>
> > Cc: Joshua Thompson <funaho@jurai.org>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Jiri Slaby <jirislaby@kernel.org>
> > Cc: stable@vger.kernel.org # v5.8+
> > References: commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> > Reported-by: Laurent Vivier <laurent@vivier.eu>
> > Signed-off-by: Finn Thain <fthain@telegraphics.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@linux-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
> 

Re: [PATCH] m68k: Fix WARNING splat in pmac_zilog driver

[Geert Uytterhoeven]

Hi Finn,

On Sat, Nov 21, 2020 at 12:47 AM Finn Thain <fthain@telegraphics.com.au> wrote:
> On Fri, 20 Nov 2020, Geert Uytterhoeven wrote:
> > On Fri, Nov 20, 2020 at 5:51 AM Finn Thain <fthain@telegraphics.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@ellerman.id.au>
> > > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > > Cc: Paul Mackerras <paulus@samba.org>
> > > Cc: Joshua Thompson <funaho@jurai.org>
> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Cc: Jiri Slaby <jirislaby@kernel.org>
> > > Cc: stable@vger.kernel.org # v5.8+
> > > References: commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> > > Reported-by: Laurent Vivier <laurent@vivier.eu>
> > > Signed-off-by: Finn Thain <fthain@telegraphics.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").

That's a long time ago ;-)
I asked because to the casual reader, it's far from obvious why the platform
device use-time is different from the platform device's resources use-time.

> 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?

Fine for me.

> > > --- 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.

OK, your main motivation is to get rid of the zero-check.
Leaving it could indeed trigger some janitorial changes by people who
don't understand the code at all, so it's good to avoid that ;-)

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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