linux-kernel - Re: [PATCH 2/2] irqchip: irq-qcom-mpm: Support passing a slice of SRAM as reg space

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Message-ID: <14350eba-edb6-0243-5451-2e2b7d1bd3fd@linaro.org>
Date:   Wed, 29 Mar 2023 15:30:12 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Shawn Guo <shawn.guo@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] irqchip: irq-qcom-mpm: Support passing a slice of
 SRAM as reg space



On 29.03.2023 15:28, Shawn Guo wrote:
> On Wed, Mar 29, 2023 at 01:06:11PM +0200, Konrad Dybcio wrote:
>>
>>
>> On 29.03.2023 05:49, Shawn Guo wrote:
>>> On Tue, Mar 28, 2023 at 12:02:53PM +0200, 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.
>>>>
>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>>> ---
>>>>  drivers/irqchip/irq-qcom-mpm.c | 30 +++++++++++++++++++++++++-----
>>>>  1 file changed, 25 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/irqchip/irq-qcom-mpm.c b/drivers/irqchip/irq-qcom-mpm.c
>>>> index d30614661eea..6fe59f4deef4 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_device.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);
>>>> +		/* Don't use devm_ioremap_resource, as we're accessing a shared region. */
>>>> +		priv->base = ioremap(res.start, resource_size(&res));
>>>
>>> Are you suggesting that other cores/drivers will also need to access
>>> the mpm slice below?
>>>
>>> 	apss_mpm: sram@1b8 {
>>> 		reg = <0x1b8 0x48>;
>>> 	};
>> Yes, the RPM M3 core. Other slices may be accessed
>> by any core at any time.
> 
> Hmm, let me reword my question.  Other than irq-qcom-mpm, is there any
> other Linux drivers that also need to request this slice region?
No.

> Otherwise, I do not understand why devm_ioremap_resource() cannot be
> used.
drivers/rpmsg/qcom_glink_rpm.c calls devm_ioremap on the entire
RPM MSG RAM.

Konrad

> 
> Shawn