linux-kernel - Re: [PATCH] drivers/amba: add reset control to primecell probe

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Date:   Fri, 2 Aug 2019 09:42:24 -0500
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Dinh Nguyen <dinh.nguyen@...el.com>
Subject: Re: [PATCH] drivers/amba: add reset control to primecell probe



On 8/2/19 9:37 AM, Rob Herring wrote:
> On Thu, Aug 1, 2019 at 12:44 PM Dinh Nguyen <dinguyen@...nel.org> wrote:
>>
>> From: Dinh Nguyen <dinh.nguyen@...el.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@...nel.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