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Message-ID: <1a3d840d-50d3-474f-89a6-e36a1cb8f5de@linaro.org>
Date:   Sat, 25 Nov 2023 16:41:22 +0100
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Subject: Re: [PATCH v6 2/2] irqchip: irq-qcom-mpm: Support passing a slice of
 SRAM as reg space
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To:     Bryan O'Donoghue <bryan.odonoghue@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Shawn Guo <shawn.guo@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>
Cc:     Marijn Suijten <marijn.suijten@somainline.org>,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org
References: <20230328-topic-msgram_mpm-v6-0-682e4855b7e2@linaro.org>
 <20230328-topic-msgram_mpm-v6-2-682e4855b7e2@linaro.org>
 <44a2b30a-7f8c-44a9-8a74-b09fee2b61b7@linaro.org>
From:   Konrad Dybcio <konrad.dybcio@linaro.org>
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On 25.11.2023 16:17, Bryan O'Donoghue wrote:
> On 25/11/2023 14:27, Konrad Dybcio wrote:
>> The MPM hardware is accessible to us from the ARM CPUs through a shared
>> memory region (RPM MSG RAM) that's also concurrently accessed by other
>> kinds of cores on the system (like modem, ADSP etc.). Modeling this
>> relation in a (somewhat) sane manner in the device tree basically
>> requires us to either present the MPM as a child of said memory region
>> (which makes little sense, as a mapped memory carveout is not a bus),
>> define nodes which bleed their register spaces into one another, or
>> passing their slice of the MSG RAM through some kind of a property.
>>
>> Go with the third option and add a way to map a region passed through
>> the "qcom,rpm-msg-ram" property as our register space.
>>
>> The current way of using 'reg' is preserved for ABI reasons.
>>
>> Acked-by: Shawn Guo <shawn.guo@linaro.org>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
>> ---
>>   drivers/irqchip/irq-qcom-mpm.c | 21 ++++++++++++++++++---
>>   1 file changed, 18 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-qcom-mpm.c b/drivers/irqchip/irq-qcom-mpm.c
>> index 7124565234a5..7115e3056aa5 100644
>> --- a/drivers/irqchip/irq-qcom-mpm.c
>> +++ b/drivers/irqchip/irq-qcom-mpm.c
>> @@ -14,6 +14,7 @@
>>   #include <linux/mailbox_client.h>
>>   #include <linux/module.h>
>>   #include <linux/of.h>
>> +#include <linux/of_address.h>
>>   #include <linux/of_platform.h>
>>   #include <linux/platform_device.h>
>>   #include <linux/pm_domain.h>
>> @@ -322,8 +323,10 @@ static int qcom_mpm_init(struct device_node *np, struct device_node *parent)
>>       struct device *dev = &pdev->dev;
>>       struct irq_domain *parent_domain;
>>       struct generic_pm_domain *genpd;
>> +    struct device_node *msgram_np;
>>       struct qcom_mpm_priv *priv;
>>       unsigned int pin_cnt;
>> +    struct resource res;
>>       int i, irq;
>>       int ret;
>>   @@ -374,9 +377,21 @@ static int qcom_mpm_init(struct device_node *np, struct device_node *parent)
>>         raw_spin_lock_init(&priv->lock);
>>   -    priv->base = devm_platform_ioremap_resource(pdev, 0);
>> -    if (IS_ERR(priv->base))
>> -        return PTR_ERR(priv->base);
>> +    /* If we have a handle to an RPM message ram partition, use it. */
>> +    msgram_np = of_parse_phandle(np, "qcom,rpm-msg-ram", 0);
>> +    if (msgram_np) {
>> +        ret = of_address_to_resource(msgram_np, 0, &res);
> 
> You are capturing the return value but doing nothing with it.
Oops you're right
> 
> One of
> 
> if (ret) {
>     of_node_put(msgram_np);
>     return ret;
> }
> 
> or just drop the ret =
> 
> if you are sure of_address_to_resource() can never return an error for your use-case.
Never say never!

Konrad