Re: [PATCH resend] mtd: maps: physmap: Add minimal Runtime PM support

[Kevin Hilman <khilman@xxxxxxxxxxxx>]

Geert Uytterhoeven <geert+renesas@xxxxxxxxx> writes:

> Add minimal runtime PM support (enable on probe, disable on remove), to
> ensure proper operation with a parent device that uses runtime PM.
>
> This is needed on systems where the FLASH is connected to a bus
> controller that is contained in a PM domain and/or has a gateable
> functional clock.  In such cases, before accessing any device connected
> to the external bus, the PM domain must be powered up, and/or the
> functional clock must be enabled, which is typically handled through
> runtime PM by the bus controller driver.
>
> An example of this is the Renesas APE6-EVM development board, which has
> an Ethernet controller and a CFI FLASH connected to the Bus State
> Controller (BSC) of an R-Mobile APE6 SoC.
> As long as the Ethernet driver, which had Runtime PM support since
> commit 3a611e26e958b037 ("net/smsc911x: Add minimal runtime PM
> support"), keeps the BSC powered, accessing the FLASH works.
> When the ethernet node in r8a73a4-ape6evm.dts is disabled, the BSC is
> never powered up, and the kernel crashes when trying to access the
> FLASH:
>
>     Unhandled fault: imprecise external abort (0x1406) at 0x00000000
>     pgd = (ptrval)
>     [00000000] *pgd=7fef2835
>     Internal error: : 1406 [#1] SMP ARM
>     CPU: 0 PID: 122 Comm: hd Tainted: G        W         5.5.0-rc1-ape6evm-00814-g38ca966db25b9dbd-dirty #136
>     Hardware name: Generic R8A73A4 (Flattened Device Tree)
>     PC is at chip_ready+0x12c/0x380
>     LR is at chip_ready+0x10c/0x380
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Reviewed-by: Kevin Hilman <khilman@xxxxxxxxxxxx>

> ---
> Probably the device should be powered down after probing, and powered
> up/down on-demand in the various {get,put}_chip() functions.  However,
> that is an optimization which touches more intimidate details of the
> internal MTD API, and can be done later.

Agreed.  Without that, the BSC (in your example) will never get powered
off as long as there's a flash device pobed.

Kevin

> ---
>  drivers/mtd/maps/physmap-core.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mtd/maps/physmap-core.c b/drivers/mtd/maps/physmap-core.c
> index a9f7964e2edb6668..8f7f966fa9a7ee8a 100644
> --- a/drivers/mtd/maps/physmap-core.c
> +++ b/drivers/mtd/maps/physmap-core.c
> @@ -38,6 +38,7 @@
>  #include <linux/mtd/cfi_endian.h>
>  #include <linux/io.h>
>  #include <linux/of_device.h>
> +#include <linux/pm_runtime.h>
>  #include <linux/gpio/consumer.h>
>  
>  #include "physmap-gemini.h"
> @@ -64,16 +65,16 @@ static int physmap_flash_remove(struct platform_device *dev)
>  {
>  	struct physmap_flash_info *info;
>  	struct physmap_flash_data *physmap_data;
> -	int i, err;
> +	int i, err = 0;
>  
>  	info = platform_get_drvdata(dev);
>  	if (!info)
> -		return 0;
> +		goto out;
>  
>  	if (info->cmtd) {
>  		err = mtd_device_unregister(info->cmtd);
>  		if (err)
> -			return err;
> +			goto out;
>  
>  		if (info->cmtd != info->mtds[0])
>  			mtd_concat_destroy(info->cmtd);
> @@ -88,7 +89,10 @@ static int physmap_flash_remove(struct platform_device *dev)
>  	if (physmap_data && physmap_data->exit)
>  		physmap_data->exit(dev);
>  
> -	return 0;
> +out:
> +	pm_runtime_put(&dev->dev);
> +	pm_runtime_disable(&dev->dev);
> +	return err;
>  }
>  
>  static void physmap_set_vpp(struct map_info *map, int state)
> @@ -484,13 +488,19 @@ static int physmap_flash_probe(struct platform_device *dev)
>  		return -EINVAL;
>  	}
>  
> +	pm_runtime_enable(&dev->dev);
> +	pm_runtime_get_sync(&dev->dev);
> +
>  	if (dev->dev.of_node)
>  		err = physmap_flash_of_init(dev);
>  	else
>  		err = physmap_flash_pdata_init(dev);
>  
> -	if (err)
> +	if (err) {
> +		pm_runtime_put(&dev->dev);
> +		pm_runtime_disable(&dev->dev);
>  		return err;
> +	}
>  
>  	for (i = 0; i < info->nmaps; i++) {
>  		struct resource *res;
> -- 
> 2.17.1

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