Re: [PATCH 1/2 v3] mtd/uclinux: support ROM and allow passing the base address

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello Greg,

On Fri, Jan 11, 2013 at 11:37:29PM +1000, Greg Ungerer wrote:
> On 01/11/2013 02:31 AM, Uwe Kleine-König wrote:
> >This allows to put the filesystem at a defined address in ROM allowing
> >to save more precious RAM.
> >
> >I think it's safe to default to ROM because the intention of using the
> >uclinux map is to use a romfs and so mtd-ram doesn't give you anything
> >that mtd-rom doesn't.
> >
> >Just in case I missed something a warning is added if the driver has to
> >fall back to the RAM mapping.
> >
> >Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> >---
> >Changes since v2, id:1350027693-19528-1-git-send-email-u.kleine-koenig@pengutronix.de:
> >
> >  - drop a few "ram"s from printks instead of making them "ram/rom"
> >  - fix a typo in the commit log and add rational for the introduced warning.
> >
> >Who is responsible for taking (or not) these two patches? David? Artem?
> >
> >Best regards
> >Uwe
> >
> >---
> >  drivers/mtd/maps/Kconfig   |    2 +-
> >  drivers/mtd/maps/uclinux.c |   26 +++++++++++++++++++++-----
> >  2 files changed, 22 insertions(+), 6 deletions(-)
> >
> >diff --git a/drivers/mtd/maps/Kconfig b/drivers/mtd/maps/Kconfig
> >index 2e47c2e..0dc86fc 100644
> >--- a/drivers/mtd/maps/Kconfig
> >+++ b/drivers/mtd/maps/Kconfig
> >@@ -443,7 +443,7 @@ config MTD_GPIO_ADDR
> >
> >  config MTD_UCLINUX
> >  	bool "Generic uClinux RAM/ROM filesystem support"
> >-	depends on MTD_RAM=y && (!MMU || COLDFIRE)
> >+	depends on (MTD_RAM=y || MTD_ROM=y) && (!MMU || COLDFIRE)
> >  	help
> >  	  Map driver to support image based filesystems for uClinux.
> >
> >diff --git a/drivers/mtd/maps/uclinux.c b/drivers/mtd/maps/uclinux.c
> >index 299bf88..b3a9c54 100644
> >--- a/drivers/mtd/maps/uclinux.c
> >+++ b/drivers/mtd/maps/uclinux.c
> >@@ -24,11 +24,12 @@
> >  /****************************************************************************/
> >
> >  struct map_info uclinux_ram_map = {
> >-	.name = "RAM",
> >-	.phys = (unsigned long)__bss_stop,
> >  	.size = 0,
> >  };
> >
> >+static unsigned long physaddr = -1;
> >+module_param(physaddr, ulong, S_IRUGO);
> >+
> >  static struct mtd_info *uclinux_ram_mtdinfo;
> >
> >  /****************************************************************************/
> >@@ -60,11 +61,17 @@ static int __init uclinux_mtd_init(void)
> >  	struct map_info *mapp;
> >
> >  	mapp = &uclinux_ram_map;
> >+
> >+	if (physaddr == -1)
> >+		mapp->phys = (resource_size_t)__bss_stop;
> >+	else
> >+		mapp->phys = physaddr;
> >+
> >  	if (!mapp->size)
> >  		mapp->size = PAGE_ALIGN(ntohl(*((unsigned long *)(mapp->phys + 8))));
> >  	mapp->bankwidth = 4;
> >
> >-	printk("uclinux[mtd]: RAM probe address=0x%x size=0x%x\n",
> >+	printk("uclinux[mtd]: probe address=0x%x size=0x%x\n",
> >  	       	(int) mapp->phys, (int) mapp->size);
> >
> >  	/*
> >@@ -82,7 +89,16 @@ static int __init uclinux_mtd_init(void)
> >
> >  	simple_map_init(mapp);
> >
> >-	mtd = do_map_probe("map_ram", mapp);
> >+	mapp->name = "ROM";
> >+	mtd = do_map_probe("map_rom", mapp);
> >+	if (!mtd) {
> >+		/* fall back to ram probing for compatibility reasons */
> >+		mapp->name = "RAM";
> >+		mtd = do_map_probe("map_ram", mapp);
> >+		if (mtd && IS_ENABLED(CONFIG_MTD_ROM))
> >+			pr_err("Failed to map rom, but ram succeeded. Please report this issue!\n");
> 
> I still don't like this, as per:
> 
> http://lists.infradead.org/pipermail/linux-mtd/2012-October/044612.html
I remember your concerns, but as you didn't write back on my last try to
explain why I consider the warning useful, I resent.

You wrote:

 The message is only printed if both ROM and RAM mappings are enabled.
 Many of the configs I use only have RAM mappings enabled.

Yeah, so the warning will not trigger for you. And this is correct,
because the only thing I want to catch is map_rom not being able to
provide everything needed when map_ram does.

I don't know what you would prefer. Just drop the warning? Force the
usage of map_rom by depending on (or selecting) MTD_ROM?

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
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