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SubjectRe: [PATCH] drivers/amba: add reset control to primecell probe
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On 8/2/19 9:37 AM, Rob Herring wrote:
> On Thu, Aug 1, 2019 at 12:44 PM Dinh Nguyen <dinguyen@kernel.org> wrote:
>>
>> From: Dinh Nguyen <dinh.nguyen@intel.com>
>>
>> The primecell controller on some SoCs, i.e. SoCFPGA, is held in reset by
>> default. Until recently, the DMA controller was brought out of reset by the
>> bootloader(i.e. U-Boot). But a recent change in U-Boot, the peripherals that
>> are not used are held in reset and are left to Linux to bring them out of
>> reset.
>
> You can fix this in the kernel, but any versions before this change
> will remain broken. IMO, the u-boot change should be reverted because
> it is breaking an ABI (though not a good one).
>

Right, there exists in U-Boot to support legacy platforms before this
recent change. This would be for future versions.

>> Add a mechanism for getting the reset property and de-assert the primecell
>> module from reset if found. This is a not a hard fail if the reset property
>> is not present in the device tree node, so the driver will continue to probe.
>
> I think this belongs in the AMBA bus code, not the DT code, as that is
> where we already have clock control code for similar reasons.
>

Ok.

>>
>> Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
>> ---
>> drivers/of/platform.c | 14 ++++++++++++++
>> 1 file changed, 14 insertions(+)
>>
>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> index 7801e25e6895..d8945705313d 100644
>> --- a/drivers/of/platform.c
>> +++ b/drivers/of/platform.c
>> @@ -21,6 +21,7 @@
>> #include <linux/of_irq.h>
>> #include <linux/of_platform.h>
>> #include <linux/platform_device.h>
>> +#include <linux/reset.h>
>>
>> const struct of_device_id of_default_bus_match_table[] = {
>> { .compatible = "simple-bus", },
>> @@ -229,6 +230,7 @@ static struct amba_device *of_amba_device_create(struct device_node *node,
>> struct amba_device *dev;
>> const void *prop;
>> int i, ret;
>> + struct reset_control *rstc;
>>
>> pr_debug("Creating amba device %pOF\n", node);
>>
>> @@ -270,6 +272,18 @@ static struct amba_device *of_amba_device_create(struct device_node *node,
>> goto err_free;
>> }
>>
>> + /*
>> + * reset control of the primecell block is optional
>> + * and will not fail if the reset property is not found.
>> + */
>> + rstc = of_reset_control_get_exclusive(node, "dma");
>
> 'dma' doesn't sound very generic.
>

how about 'primecell' ?

Thanks for the review!

Dinh

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