[PATCH 1/1] ARM: OMAP: gpmc: request CS address space for ethernet chips

Javier Martinez Canillas javier.martinez at collabora.co.uk
Mon Mar 11 13:57:56 EDT 2013

On 03/11/2013 06:13 PM, Jon Hunter wrote:

Hi Jon, thanks a lot for your feedback.

> On 03/10/2013 12:18 PM, Javier Martinez Canillas wrote:
>> Besides being used to interface with external memory devices,
>> the General-Purpose Memory Controller can be used to connect
>> Pseudo-SRAM devices such as ethernet controllers to OMAP2+
>> processors using the GPMC as a data bus.
>> The actual mapping between the GPMC address space and OMAP2+
>> address space is made using the GPMC DT "ranges" property.
>> But also a explicit call to gpmc_cs_request() is needed.
> One problem with gpmc_cs_request() is that it will map the chip-select
> to any physical location in the 1GB address space for the gpmc
> controller. So in other words, it will ignore the ranges property
> altogether. If you look at my code for NOR, I have added a
> gpmc_cs_remap() function to remap the cs to the location as specified by
> the device-tree.

I see, thanks for pointing this out.

> Ideally we should change gpmc_cs_request() so we can pass the desire
> base address that we want to map the gpmc cs too. I had started out that
> way but it made the code some what messy and so I opted to create a
> gpmc_cs_remap() function instead. The goal will be to get rid of
> gpmc_cs_remap() once DT migration is completed and we can change
> gpmc_cs_request() to map the cs to a specific address (see my FIXME
> comment).

By looking at gpmc_probe_onenand_child() and gpmc_probe_nand_child() I see that
these functions just allocates platform data and call gpmc_onenand_init() and
gpmc_nand_init() accordingly. So if I understood right these functions have the
same issue and need to call gpmc_cs_remap() too in order to map to the location
specified on the DT.

> Your code probably works today because the cs is setup by the bootloader
> and so when you request the cs in the kernel the mapping is not changed
> from the bootloader settings. However, if the mapping in DT (ranges
> property) is different from that setup by the bootloader then the kernel
> would probably crash because the kernel would not remap it as expected.
>> So, this patch allows an ethernet chip to be defined as an
>> GPMC child node an its chip-select memory address be requested.
>> Signed-off-by: Javier Martinez Canillas <javier.martinez at collabora.co.uk>
>> ---
>> Jon,
>> This patch assumes that we have solved somehow the issue that a
>> call to request_irq() is needed before before using a GPIO as an
>> IRQ and this is no longer the case when using from Device Trees.
>> Anyway, this is independent as how we solve this, whether is
>> using Jan's patch [1], adding a .request function pointer to
>> irq_chip as suggested by Stephen [2], or any other approach.
>> [1]: https://patchwork.kernel.org/patch/2009331/
>> [2]: http://www.mail-archive.com/linux-omap@vger.kernel.org/msg85592.html
>>  arch/arm/mach-omap2/gpmc.c |   45 ++++++++++++++++++++++++++++++++++++++++++++
>>  1 files changed, 45 insertions(+), 0 deletions(-)
>> diff --git a/arch/arm/mach-omap2/gpmc.c b/arch/arm/mach-omap2/gpmc.c
>> index 4fe9ee7..d1bf48b 100644
>> --- a/arch/arm/mach-omap2/gpmc.c
>> +++ b/arch/arm/mach-omap2/gpmc.c
>> @@ -29,6 +29,7 @@
>>  #include <linux/of.h>
>>  #include <linux/of_mtd.h>
>>  #include <linux/of_device.h>
>> +#include <linux/of_address.h>
>>  #include <linux/mtd/nand.h>
>>  #include <linux/platform_data/mtd-nand-omap2.h>
>> @@ -1296,6 +1297,42 @@ static int gpmc_probe_onenand_child(struct platform_device *pdev,
>>  }
>>  #endif
>> +static int gpmc_probe_ethernet_child(struct platform_device *pdev,
>> +				     struct device_node *child)
>> +{
>> +	int ret, cs;
>> +	unsigned long base;
>> +	struct resource res;
>> +	struct platform_device *of_dev;
>> +
>> +	if (of_property_read_u32(child, "reg", &cs) < 0) {
>> +		dev_err(&pdev->dev, "%s has no 'reg' property\n",
>> +			child->full_name);
>> +		return -ENODEV;
>> +	}
>> +
>> +	if (of_address_to_resource(child, 0, &res)) {
>> +		dev_err(&pdev->dev, "%s has malformed 'reg' property\n",
>> +			child->full_name);
>> +		return -ENODEV;
>> +	}
>> +
>> +	ret = gpmc_cs_request(cs, resource_size(&res), &base);
>> +	if (IS_ERR_VALUE(ret)) {
>> +		dev_err(&pdev->dev, "cannot request GPMC CS %d\n", cs);
>> +		return ret;
>> +	}
>> +
>> +	of_dev = of_platform_device_create(child, NULL, &pdev->dev);
>> +	if (!of_dev) {
>> +		dev_err(&pdev->dev, "cannot create platform device for %s\n",
>> +			child->full_name);
>> +		return -ENODEV;
>> +	}
>> +
>> +	return 0;
>> +}
> So this function does not setup the cs at all and so that means you are
> dependent on having the bootloader configure the cs. I would really like
> to get away from that sort of dependency. In fact I am wondering if we
> could make the gpmc_probe_nor() function a gpmc_probe_generic() that we
> can use for both nor and ethernet as we are doing very similar things
> (if we add the timings and gpmc settings to the ethernet binding).

Yes, I also thought about a gmpc_probe_generic() for all GMPC child nodes since
the chip-select setup is the same for all of them.

The problem I saw was that gpmc_probe_{onenand,nand}_child() were just wrappers
around gpmc_{onenand,nand}_init() and since the init functions call
gpmc_cs_request(), I couldn't have a generic probe that call gpmc_cs_request()
for all childs.

But since we should probably have to change this to call gpmc_cs_remap() besides
gpmc_cs_request(), I think is better to not use gpmc_{onenand,nand}_init() at
all and make this somehow generic.

Actually, since the mapping (and the IORESOURCE_MEM struct resource allocation)
is made by the DT core using the "ranges" property. I wonder if we could add
some callback function (e.g: .range_request() ) that can be set by memory
controllers that want to take an action (such as calling gpmc_cs_request() and
gpmc_cs_remap() ) once each element in the "ranges" vector is processed by the
DT core.

> Also I think we need to add some DT binding documentation for this as well.


> Cheers
> Jon

Best regards,

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