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Subject: Re: [v1] PCI: mediatek: Remove MSI inner domain
To:     Honghui Zhang <honghui.zhang@mediatek.com>,
        Jianjun Wang <jianjun.wang@mediatek.com>
Cc:     ryder.lee@mediatek.com, lorenzo.pieralisi@arm.com,
        bhelgaas@google.com, matthias.bgg@gmail.com,
        linux-pci@vger.kernel.org, linux-mediatek@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        youlin.pei@mediatek.com
References: <1548149855-3225-1-git-send-email-jianjun.wang@mediatek.com>
 <1548926367.4980.14.camel@mhfsdcap03>
From:   Marc Zyngier <marc.zyngier@arm.com>
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Organization: ARM Ltd
Message-ID: <10e8e731-5749-f6fb-eb33-ab67aa0e2c3f@arm.com>
Date:   Thu, 31 Jan 2019 09:44:48 +0000
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On 31/01/2019 09:19, Honghui Zhang wrote:
> On Tue, 2019-01-22 at 17:37 +0800, Jianjun Wang wrote:
>> There is no need to create the inner domain as a parent for MSI domian,
>> some feature has been implemented by MSI framework.
>>
>> Remove the inner domain and its irq chip, it will be more closer to
>> hardware implementation.

This is not about being closer to any HW implementation. This is about
having a uniform way to deal with MSI controllers, no matter how they
are implemented by the HW.

So maybe you could start by explaining what this is trying to achieve.

>>
> Hi, jianjun, I'm not quite familiar with the irq_chip framework, It was
> under Marc's great help with the first version of irq_chip solution
> code. I would like you to add him for the review.
> 
> Thanks.
> 
>> Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
>> ---
>>  drivers/pci/controller/pcie-mediatek.c | 86 +++++++++++---------------
>>  1 file changed, 37 insertions(+), 49 deletions(-)
>>
>> diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
>> index 8d05df56158b..f996a9a6331f 100644
>> --- a/drivers/pci/controller/pcie-mediatek.c
>> +++ b/drivers/pci/controller/pcie-mediatek.c
>> @@ -169,7 +169,6 @@ struct mtk_pcie_soc {
>>   * @slot: port slot
>>   * @irq: GIC irq
>>   * @irq_domain: legacy INTx IRQ domain
>> - * @inner_domain: inner IRQ domain
>>   * @msi_domain: MSI IRQ domain
>>   * @lock: protect the msi_irq_in_use bitmap
>>   * @msi_irq_in_use: bit map for assigned MSI IRQ
>> @@ -190,7 +189,6 @@ struct mtk_pcie_port {
>>  	u32 slot;
>>  	int irq;
>>  	struct irq_domain *irq_domain;
>> -	struct irq_domain *inner_domain;
>>  	struct irq_domain *msi_domain;
>>  	struct mutex lock;
>>  	DECLARE_BITMAP(msi_irq_in_use, MTK_MSI_IRQS_NUM);
>> @@ -418,22 +416,15 @@ static void mtk_msi_ack_irq(struct irq_data *data)
>>  	u32 hwirq = data->hwirq;
>>  
>>  	writel(1 << hwirq, port->base + PCIE_IMSI_STATUS);
>> +	writel(MSI_STATUS, port->base + PCIE_INT_STATUS);
>>  }
>>  
>> -static struct irq_chip mtk_msi_bottom_irq_chip = {
>> -	.name			= "MTK MSI",
>> -	.irq_compose_msi_msg	= mtk_compose_msi_msg,
>> -	.irq_set_affinity	= mtk_msi_set_affinity,
>> -	.irq_ack		= mtk_msi_ack_irq,
>> -};
>> -
>> -static int mtk_pcie_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
>> -				     unsigned int nr_irqs, void *args)
>> +static irq_hw_number_t mtk_pcie_msi_get_hwirq(struct msi_domain_info *info,
>> +					      msi_alloc_info_t *arg)
>>  {
>> -	struct mtk_pcie_port *port = domain->host_data;
>> -	unsigned long bit;
>> +	struct mtk_pcie_port *port = info->chip_data;
>> +	irq_hw_number_t bit;
>>  
>> -	WARN_ON(nr_irqs != 1);
>>  	mutex_lock(&port->lock);
>>  
>>  	bit = find_first_zero_bit(port->msi_irq_in_use, MTK_MSI_IRQS_NUM);
>> @@ -446,18 +437,14 @@ static int mtk_pcie_irq_domain_alloc(struct irq_domain *domain, unsigned int vir
>>  
>>  	mutex_unlock(&port->lock);
>>  
>> -	irq_domain_set_info(domain, virq, bit, &mtk_msi_bottom_irq_chip,
>> -			    domain->host_data, handle_edge_irq,
>> -			    NULL, NULL);
>> -
>> -	return 0;
>> +	return bit;

Why do you need to override the get_hwirq method? Using the generic
PCI/MSI version has the advantage of giving you a universal encoding
which makes debugging much easier.

>>  }
>>  
>> -static void mtk_pcie_irq_domain_free(struct irq_domain *domain,
>> -				     unsigned int virq, unsigned int nr_irqs)
>> +static void mtk_pcie_msi_free(struct irq_domain *domain,
>> +			      struct msi_domain_info *info, unsigned int virq)
>>  {
>>  	struct irq_data *d = irq_domain_get_irq_data(domain, virq);
>> -	struct mtk_pcie_port *port = irq_data_get_irq_chip_data(d);
>> +	struct mtk_pcie_port *port = info->chip_data;
>>  
>>  	mutex_lock(&port->lock);
>>  
>> @@ -468,46 +455,50 @@ static void mtk_pcie_irq_domain_free(struct irq_domain *domain,
>>  		__clear_bit(d->hwirq, port->msi_irq_in_use);
>>  
>>  	mutex_unlock(&port->lock);
>> -
>> -	irq_domain_free_irqs_parent(domain, virq, nr_irqs);
>>  }
>>  
>> -static const struct irq_domain_ops msi_domain_ops = {
>> -	.alloc	= mtk_pcie_irq_domain_alloc,
>> -	.free	= mtk_pcie_irq_domain_free,
>> +static struct msi_domain_ops mtk_msi_domain_ops = {
>> +	.get_hwirq	= mtk_pcie_msi_get_hwirq,
>> +	.msi_free	= mtk_pcie_msi_free,
>>  };
>>  
>>  static struct irq_chip mtk_msi_irq_chip = {
>> -	.name		= "MTK PCIe MSI",
>> -	.irq_ack	= irq_chip_ack_parent,
>> -	.irq_mask	= pci_msi_mask_irq,
>> -	.irq_unmask	= pci_msi_unmask_irq,
>> +	.name			= "MTK PCIe",
>> +	.irq_compose_msi_msg	= mtk_compose_msi_msg,
>> +	.irq_write_msi_msg	= pci_msi_domain_write_msg,
>> +	.irq_set_affinity	= mtk_msi_set_affinity,
>> +	.irq_ack		= mtk_msi_ack_irq,
>> +	.irq_mask		= pci_msi_mask_irq,
>> +	.irq_unmask		= pci_msi_unmask_irq,
>>  };
>>  
>>  static struct msi_domain_info mtk_msi_domain_info = {
>> -	.flags	= (MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
>> -		   MSI_FLAG_PCI_MSIX),
>> -	.chip	= &mtk_msi_irq_chip,
>> +	.flags		= (MSI_FLAG_USE_DEF_DOM_OPS |
>> +			   MSI_FLAG_USE_DEF_CHIP_OPS | MSI_FLAG_PCI_MSIX),
>> +	.ops		= &mtk_msi_domain_ops,
>> +	.chip		= &mtk_msi_irq_chip,
>> +	.handler	= handle_edge_irq,
>> +	.handler_name	= "MSI",
>>  };
>>  
>>  static int mtk_pcie_allocate_msi_domains(struct mtk_pcie_port *port)
>>  {
>> -	struct fwnode_handle *fwnode = of_node_to_fwnode(port->pcie->dev->of_node);
>> +	struct device *dev = port->pcie->dev;
>> +	struct fwnode_handle *fwnode = of_node_to_fwnode(dev->of_node);
>> +	struct msi_domain_info *info;
>>  
>>  	mutex_init(&port->lock);
>>  
>> -	port->inner_domain = irq_domain_create_linear(fwnode, MTK_MSI_IRQS_NUM,
>> -						      &msi_domain_ops, port);
>> -	if (!port->inner_domain) {
>> -		dev_err(port->pcie->dev, "failed to create IRQ domain\n");
>> +	info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
>> +	if (!info)
>>  		return -ENOMEM;
>> -	}
>>  
>> -	port->msi_domain = pci_msi_create_irq_domain(fwnode, &mtk_msi_domain_info,
>> -						     port->inner_domain);
>> +	memcpy(info, &mtk_msi_domain_info, sizeof(*info));
>> +	info->chip_data = port;
>> +
> 
> I'm not really like this memcpy of msi_domain_info, but I do not have a
> better idea to prevent the mixed of mtk_pcie_port data.

So we're basically trading an indirection for another. What's the gain?

> 
>> +	port->msi_domain = pci_msi_create_irq_domain(fwnode, info, NULL);
>>  	if (!port->msi_domain) {
>> -		dev_err(port->pcie->dev, "failed to create MSI domain\n");
>> -		irq_domain_remove(port->inner_domain);
>> +		dev_err(dev, "failed to create MSI domain\n");
>>  		return -ENOMEM;
>>  	}
>>  
>> @@ -541,8 +532,6 @@ static void mtk_pcie_irq_teardown(struct mtk_pcie *pcie)
>>  		if (IS_ENABLED(CONFIG_PCI_MSI)) {
>>  			if (port->msi_domain)
>>  				irq_domain_remove(port->msi_domain);
>> -			if (port->inner_domain)
>> -				irq_domain_remove(port->inner_domain);
>>  		}
>>  
>>  		irq_dispose_mapping(port->irq);
>> @@ -619,12 +608,11 @@ static void mtk_pcie_intr_handler(struct irq_desc *desc)
>>  
>>  			while ((imsi_status = readl(port->base + PCIE_IMSI_STATUS))) {
>>  				for_each_set_bit(bit, &imsi_status, MTK_MSI_IRQS_NUM) {
>> -					virq = irq_find_mapping(port->inner_domain, bit);
>> +					virq = irq_find_mapping(
>> +							port->msi_domain, bit);
>>  					generic_handle_irq(virq);
>>  				}
>>  			}
>> -			/* Clear MSI interrupt status */
>> -			writel(MSI_STATUS, port->base + PCIE_INT_STATUS);
>>  		}
> 
> why change this irq status clear flow?

I think this is trying move everything to the irq_ack callback. But
that's a change of semantics, and I'd like it explained. It certainly
feels wrong.

Overall, this patch as it stands (without any real explanation) doesn't
feel me with confidence. It introduces significant differences in the
way we build PCI/MSI domains, and I'd like to understand why.

Thanks,

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