[PATCH AUTOSEL 4.19 03/11] irqchip/sifive-plic: Add missing thead, c900-plic match string

[PATCH AUTOSEL 4.19 03/11] irqchip/sifive-plic: Add missing thead, c900-plic match string

[Sasha Levin]

From: Guo Ren <guoren@linux.alibaba.com>

[ Upstream commit 1d4df649cbb4b26d19bea38ecff4b65b10a1bbca ]

The thead,c900-plic has been used in opensbi to distinguish
PLIC [1]. Although PLICs have the same behaviors in Linux,
they are different hardware with some custom initializing in
firmware(opensbi).

Qute opensbi patch commit-msg by Samuel:

  The T-HEAD PLIC implementation requires setting a delegation bit
  to allow access from S-mode. Now that the T-HEAD PLIC has its own
  compatible string, set this bit automatically from the PLIC driver,
  instead of reaching into the PLIC's MMIO space from another driver.

[1]: https://github.com/riscv-software-src/opensbi/commit/78c2b19218bd62653b9fb31623a42ced45f38ea6

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Anup Patel <anup@brainfault.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Samuel Holland <samuel@sholland.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220130135634.1213301-3-guoren@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/irqchip/irq-sifive-plic.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index 532e9d68c7042..767cdd3f773bb 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -258,3 +258,4 @@ static int __init plic_init(struct device_node *node,
 
 IRQCHIP_DECLARE(sifive_plic, "sifive,plic-1.0.0", plic_init);
 IRQCHIP_DECLARE(riscv_plic0, "riscv,plic0", plic_init); /* for legacy systems */
+IRQCHIP_DECLARE(thead_c900_plic, "thead,c900-plic", plic_init); /* for firmware driver */
-- 
2.34.1


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Re: [PATCH AUTOSEL 4.19 03/11] irqchip/sifive-plic: Add missing thead,c900-plic match string

[Pavel Machek]

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Hi!

> [ Upstream commit 1d4df649cbb4b26d19bea38ecff4b65b10a1bbca ]
> 
> The thead,c900-plic has been used in opensbi to distinguish
> PLIC [1]. Although PLICs have the same behaviors in Linux,
> they are different hardware with some custom initializing in
> firmware(opensbi).
> 
> Qute opensbi patch commit-msg by Samuel:
> 
>   The T-HEAD PLIC implementation requires setting a delegation bit
>   to allow access from S-mode. Now that the T-HEAD PLIC has its own
>   compatible string, set this bit automatically from the PLIC driver,
>   instead of reaching into the PLIC's MMIO space from another driver.
> 
> [1]: https://github.com/riscv-software-src/opensbi/commit/78c2b19218bd62653b9fb31623a42ced45f38ea6
>

The "thead,c900-plic" string is added into single place in the
kernel. This means that a) it will probably not do anything useful in
-stable kernels and b) it is certainly missing documentation etc.

In mainline, string is documented in
Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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Re: [PATCH AUTOSEL 4.19 03/11] irqchip/sifive-plic: Add missing thead,c900-plic match string

[Marc Zyngier]

On 2022-02-20 09:54, Pavel Machek wrote:
> Hi!
> 
>> [ Upstream commit 1d4df649cbb4b26d19bea38ecff4b65b10a1bbca ]
>> 
>> The thead,c900-plic has been used in opensbi to distinguish
>> PLIC [1]. Although PLICs have the same behaviors in Linux,
>> they are different hardware with some custom initializing in
>> firmware(opensbi).
>> 
>> Qute opensbi patch commit-msg by Samuel:
>> 
>>   The T-HEAD PLIC implementation requires setting a delegation bit
>>   to allow access from S-mode. Now that the T-HEAD PLIC has its own
>>   compatible string, set this bit automatically from the PLIC driver,
>>   instead of reaching into the PLIC's MMIO space from another driver.
>> 
>> [1]: 
>> https://github.com/riscv-software-src/opensbi/commit/78c2b19218bd62653b9fb31623a42ced45f38ea6
>> 
> 
> The "thead,c900-plic" string is added into single place in the
> kernel. This means that a) it will probably not do anything useful in
> -stable kernels and b) it is certainly missing documentation etc.
> 
> In mainline, string is documented in
> Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml

(b) is certainly true. And to make the above comment useful, the missing
patch is 321a8be37e1a ("dt-bindings: update riscv plic compatible
string").

Regarding (a), the DT is provided by the firmware (as it should
be on any reasonable platform). As such, no need for this string to be
mentioned anywhere else but in the documentation.

Now, the real question is where there is any point in backporting
this to such an old kernel, as this HW is unlikely to ever run it.

         M.
-- 
Jazz is not dead. It just smells funny...

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