[PATCH] powerpc/fsl_lbc: Explicitly populate bus

[PATCH] powerpc/fsl_lbc: Explicitly populate bus

[J. Neuschäfer via B4 Relay]

From: "J. Neuschäfer" <j.ne@posteo.net>

Historically, devicetree nodes representing the Freescale Enhanced
Local Bus Controller (eLBC) have compatible strings such as:

    compatible = "fsl,mpc8313-elbc", "fsl,elbc", "simple-bus";

The "simple-bus" string causes the bus to be populated, and the memory
devices contained within it to be discovered. The eLBC bus (as
represented in device trees) differs from a simple-bus in a few ways,
though:

 - Addresses are not simple/linear: The first cell of an address is a
   chip select, the second is an linear address within the space thus
   selected. Representing 1,0 as 100000000, for example, would decrease
   readability[1].
 - It is expected that the devices on a simple-bus "can be accessed
   directly without additional configuration required"[2], but the eLBC
   needs some configuration.

To accommodate devicetrees that declare an eLBC without "simple-bus",
explicitly populate the bus in the eLBC driver.

[1]: dtc makes such a suggestion opon encountering an eLBC
[2]: Quoting the Devicetree Specification Release v0.3

Signed-off-by: J. Neuschäfer <j.ne@posteo.net>
---
 arch/powerpc/sysdev/fsl_lbc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/sysdev/fsl_lbc.c b/arch/powerpc/sysdev/fsl_lbc.c
index 217cea150987df1e1b5c6dbf9e9a1607dd5ce49b..2007ced997fcf0c7059e5b780893b530764dc8b2 100644
--- a/arch/powerpc/sysdev/fsl_lbc.c
+++ b/arch/powerpc/sysdev/fsl_lbc.c
@@ -20,6 +20,7 @@
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
+#include <linux/of_platform.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/platform_device.h>
@@ -336,7 +337,7 @@ static int fsl_lbc_ctrl_probe(struct platform_device *dev)
 	/* Enable interrupts for any detected events */
 	out_be32(&fsl_lbc_ctrl_dev->regs->lteir, LTEIR_ENABLE);
 
-	return 0;
+	return devm_of_platform_populate(&dev->dev);
 
 err1:
 	free_irq(fsl_lbc_ctrl_dev->irq[0], fsl_lbc_ctrl_dev);

---
base-commit: 7ccde445dddcca030cd6ed66974bb80915ad9dd5
change-id: 20250209-localbus-94a6ebb04c12

Best regards,
-- 
J. Neuschäfer <j.ne@posteo.net>

Re: [PATCH] powerpc/fsl_lbc: Explicitly populate bus

[J. Neuschäfer]

On Sun, Feb 09, 2025 at 10:58:50PM +0100, J. Neuschäfer via B4 Relay wrote:
> From: "J. Neuschäfer" <j.ne@posteo.net>
> 
> Historically, devicetree nodes representing the Freescale Enhanced
> Local Bus Controller (eLBC) have compatible strings such as:
> 
>     compatible = "fsl,mpc8313-elbc", "fsl,elbc", "simple-bus";
> 
> The "simple-bus" string causes the bus to be populated, and the memory
> devices contained within it to be discovered. The eLBC bus (as
> represented in device trees) differs from a simple-bus in a few ways,
> though:
> 
>  - Addresses are not simple/linear: The first cell of an address is a
>    chip select, the second is an linear address within the space thus
>    selected. Representing 1,0 as 100000000, for example, would decrease
>    readability[1].
>  - It is expected that the devices on a simple-bus "can be accessed
>    directly without additional configuration required"[2], but the eLBC
>    needs some configuration.
> 
> To accommodate devicetrees that declare an eLBC without "simple-bus",
> explicitly populate the bus in the eLBC driver.
> 
> [1]: dtc makes such a suggestion opon encountering an eLBC
> [2]: Quoting the Devicetree Specification Release v0.3
> 
> Signed-off-by: J. Neuschäfer <j.ne@posteo.net>
> ---

Due to advice from Crystal Wood and Rob Herring[1], I reached the
conclusion that this patch is not necessary.

[1]: https://lore.kernel.org/lkml/Z7ILej_AJYot_wKP@probook/

>  arch/powerpc/sysdev/fsl_lbc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/sysdev/fsl_lbc.c b/arch/powerpc/sysdev/fsl_lbc.c
> index 217cea150987df1e1b5c6dbf9e9a1607dd5ce49b..2007ced997fcf0c7059e5b780893b530764dc8b2 100644
> --- a/arch/powerpc/sysdev/fsl_lbc.c
> +++ b/arch/powerpc/sysdev/fsl_lbc.c
> @@ -20,6 +20,7 @@
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>  #include <linux/of_irq.h>
> +#include <linux/of_platform.h>
>  #include <linux/slab.h>
>  #include <linux/sched.h>
>  #include <linux/platform_device.h>
> @@ -336,7 +337,7 @@ static int fsl_lbc_ctrl_probe(struct platform_device *dev)
>  	/* Enable interrupts for any detected events */
>  	out_be32(&fsl_lbc_ctrl_dev->regs->lteir, LTEIR_ENABLE);
>  
> -	return 0;
> +	return devm_of_platform_populate(&dev->dev);
>  
>  err1:
>  	free_irq(fsl_lbc_ctrl_dev->irq[0], fsl_lbc_ctrl_dev);
> 
> ---
> base-commit: 7ccde445dddcca030cd6ed66974bb80915ad9dd5
> change-id: 20250209-localbus-94a6ebb04c12
> 
> Best regards,
> -- 
> J. Neuschäfer <j.ne@posteo.net>
> 
>