Re: [PATCH v5 4/8] memory: Add STM32 Octo Memory Manager driver

[Krzysztof Kozlowski <krzk@kernel.org>]

On 12/03/2025 15:23, Patrice CHOTARD wrote:
>>> +static int stm32_omm_disable_child(struct device *dev)
>>> +{
>>> +	struct stm32_omm *omm = dev_get_drvdata(dev);
>>> +	struct reset_control *reset;
>>> +	int ret;
>>> +	u8 i;
>>> +
>>> +	for (i = 0; i < omm->nb_child; i++) {
>>> +		ret = clk_prepare_enable(omm->child[i].clk);
>>> +		if (ret) {
>>> +			dev_err(dev, "Can not enable clock\n");
>>> +			return ret;
>>> +		}
>>> +
>>> +		reset = of_reset_control_get_exclusive(omm->child[i].node, 0);
>>> +		if (IS_ERR(reset)) {
>>> +			dev_err(dev, "Can't get child reset\n");
>>
>> Why do you get reset of child? Parent is not suppposed to poke there.
>> You might not have the reset there in the first place and it would not
>> be an error.
> 
> By ressetting child (OSPI), we ensure they are disabled and in a known state.
> See the comment below.
> 
>>
>>
>>> +			return PTR_ERR(reset);
>>> +		};
>>> +
>>> +		/* reset OSPI to ensure CR_EN bit is set to 0 */
>>> +		reset_control_assert(reset);
>>> +		udelay(2);
>>> +		reset_control_deassert(reset);
>>
>> No, the child should handle this, not parent.
> 
> Octo Memory Manager can only be configured if both child are disabled.
> That's why here, parent handles this.

So if device by any chance started and is doing some useful work, then
you cancel that work and reset it?

And what if child does not have reset line? Your binding allows that, so
how is it supposed to work then?

This also leads me to questions about bindings - if you need to assert
some reset, doesn't it mean that these resets are also coming through
this device so they are part of this device node?


> 
>>
>>> +
>>> +		reset_control_put(reset);
>>> +		clk_disable_unprepare(omm->child[i].clk);
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int stm32_omm_probe(struct platform_device *pdev)
>>> +{
>>> +	struct platform_device *vdev;
>>> +	struct device *dev = &pdev->dev;
>>> +	struct stm32_omm *omm;
>>> +	struct clk *clk;
>>> +	int ret;
>>> +	u8 child_access_granted = 0;
>>
>> Keep inits/assignments together
> 
> ok
> 
>>
>>> +	u8 i, j;
>>> +	bool child_access[OMM_CHILD_NB];
>>> +
>>> +	omm = devm_kzalloc(dev, sizeof(*omm), GFP_KERNEL);
>>> +	if (!omm)
>>> +		return -ENOMEM;
>>> +
>>> +	omm->io_base = devm_platform_ioremap_resource_byname(pdev, "regs");
>>> +	if (IS_ERR(omm->io_base))
>>> +		return PTR_ERR(omm->io_base);
>>> +
>>> +	omm->mm_res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "memory_map");
>>> +	if (IS_ERR(omm->mm_res))
>>> +		return PTR_ERR(omm->mm_res);
>>> +
>>> +	/* check child's access */
>>> +	for_each_child_of_node_scoped(dev->of_node, child) {
>>> +		if (omm->nb_child >= OMM_CHILD_NB) {
>>> +			dev_err(dev, "Bad DT, found too much children\n");
>>> +			ret = -E2BIG;
>>> +			goto err_clk_release;
>>> +		}
>>> +
>>> +		if (!of_device_is_compatible(child, "st,stm32mp25-ospi")) {
>>> +			ret = -EINVAL;
>>> +			goto err_clk_release;
>>> +		}
>>> +
>>> +		ret = stm32_omm_check_access(dev, child);
>>> +		if (ret < 0 && ret != -EACCES)
>>> +			goto err_clk_release;
>>> +
>>> +		child_access[omm->nb_child] = false;
>>> +		if (!ret) {
>>> +			child_access_granted++;
>>> +			child_access[omm->nb_child] = true;
>>> +		}
>>> +
>>> +		omm->child[omm->nb_child].node = child;
>>> +
>>> +		clk = of_clk_get(child, 0);
>>
>> Why are you taking children clock? And why with this API, not clk_get?
> 
> I need children's clock to reset them.


The device driver should reset its device. It is not a discoverable bus,
that would explain power sequencing from the parent.

> Why of_clk_get() usage is a problem here ? i can't get your point ?

Because it is not the API which device drivers should use. You should
use clk_get or devm_clk_get.


> 
>> This looks like mixing clock provider in the clock consumer.
>>
>>> +		if (IS_ERR(clk)) {
>>> +			dev_err(dev, "Can't get child clock\n");
>>
>> Syntax is always return dev_err_probe (or ret = dev_err_probe).
> 
> ok
> 
>>
>>> +			ret = PTR_ERR(clk);
>>> +			goto err_clk_release;
>>> +		};
>>> +
>>> +		omm->child[omm->nb_child].clk = clk;
>>> +		omm->nb_child++;
>>> +	}
>>> +
>>> +	if (omm->nb_child != OMM_CHILD_NB) {
>>> +		ret = -EINVAL;
>>> +		goto err_clk_release;
>>> +	}
>>> +
>>> +	platform_set_drvdata(pdev, omm);
>>> +
>>> +	pm_runtime_enable(dev);
>>> +
>>> +	/* check if OMM's resource access is granted */
>>> +	ret = stm32_omm_check_access(dev, dev->of_node);
>>> +	if (ret < 0 && ret != -EACCES)
>>> +		goto err_clk_release;
>>> +
>>> +	if (!ret && child_access_granted == OMM_CHILD_NB) {
>>> +		/* Ensure both OSPI instance are disabled before configuring OMM */
>>> +		ret = stm32_omm_disable_child(dev);
>>> +		if (ret)
>>> +			goto err_clk_release;
>>> +
>>> +		ret = stm32_omm_configure(dev);
>>> +		if (ret)
>>> +			goto err_clk_release;
>>> +	} else {
>>> +		dev_dbg(dev, "Octo Memory Manager resource's access not granted\n");
>>> +		/*
>>> +		 * AMCR can't be set, so check if current value is coherent
>>> +		 * with memory-map areas defined in DT
>>> +		 */
>>> +		ret = stm32_omm_set_amcr(dev, false);
>>> +		if (ret)
>>> +			goto err_clk_release;
>>> +	}
>>> +
>>> +	/* for each child, if resource access is granted and status "okay", probe it */
>>> +	for (i = 0; i < omm->nb_child; i++) {
>>> +		if (!child_access[i] || !of_device_is_available(omm->child[i].node))
>>
>> If you have a device available, why do you create one more platform device?
>>
>>> +			continue;
>>> +
>>> +		vdev = of_platform_device_create(omm->child[i].node, NULL, NULL);
>>
>> Why you cannot just populate the children?
> 
> I can't use of_platform_populate(), by default it will populate all OMM's child.
> Whereas here, we want to probe only the OMM's child which match our criteria.  


Why wouldn't you populate everyone? The task of bus driver is not to
filter out DT. If you got such DT - with all device nodes - you are
expected to populate all of them. Otherwise, if you do not want all of
them, it is expected that firmware or bootloader will give you DT
without these nodes.

Best regards,
Krzysztof