linux-kernel - Re: [PATCH v3] PCI: xilinx-nwl: Fix Multi MSI data programming

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Date:   Mon, 3 Jun 2019 09:49:42 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        rgummal@...inx.com
Subject: Re: [PATCH v3] PCI: xilinx-nwl: Fix Multi MSI data programming

On 31/05/2019 17:09, Lorenzo Pieralisi wrote:
> [+Marc]
> 
> On Wed, May 29, 2019 at 06:07:49PM +0530, Bharat Kumar Gogada wrote:
>> The current Multi MSI data programming fails if multiple end points
>> requesting MSI and multi MSI are connected with switch, i.e the current
>> multi MSI data being given is not considering the number of vectors
>> being requested in case of multi MSI.
>> Ex: Two EP's connected via switch, EP1 requesting single MSI first,
>> EP2 requesting Multi MSI of count four. The current code gives
>> MSI data 0x0 to EP1 and 0x1 to EP2, but EP2 can modify lower two bits
>> due to which EP2 also sends interrupt with MSI data 0x0 which results
>> in always invoking virq of EP1 due to which EP2 MSI interrupt never
>> gets handled.
> 
> If this is a problem it is not the only driver where it should be fixed
> it seems. CC'ed Marc in case I have missed something in relation to MSI
> IRQs but AFAIU it looks like HW is allowed to toggled bits (according to
> bits[6:4] in Message Control for MSI) in the MSI data, given that the
> data written is the hwirq number (in this specific MSI controller)
> it ought to be fixed.

Yeah, it looks like a number of MSI controllers could be quite broken
in this particular area.

> 
> The commit log and patch should be rewritten (I will do that) but
> first I would like to understand if there are more drivers to be
> updated.
> 
> Lorenzo
> 
>> Fix Multi MSI data programming with required alignment by
>> using number of vectors being requested.
>>
>> Fixes: ab597d35ef11 ("PCI: xilinx-nwl: Add support for Xilinx NWL PCIe
>> Host Controller")
>> Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
>> ---
>> V3:
>>  - Added example description of the issue
>> ---
>>  drivers/pci/controller/pcie-xilinx-nwl.c | 11 ++++++++++-
>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/pcie-xilinx-nwl.c b/drivers/pci/controller/pcie-xilinx-nwl.c
>> index 81538d7..8efcb8a 100644
>> --- a/drivers/pci/controller/pcie-xilinx-nwl.c
>> +++ b/drivers/pci/controller/pcie-xilinx-nwl.c
>> @@ -483,7 +483,16 @@ static int nwl_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
>>  	int i;
>>  
>>  	mutex_lock(&msi->lock);
>> -	bit = bitmap_find_next_zero_area(msi->bitmap, INT_PCI_MSI_NR, 0,
>> +
>> +	/*
>> +	 * Multi MSI count is requested in power of two
>> +	 * Check if multi msi is requested
>> +	 */
>> +	if (nr_irqs % 2 == 0)
>> +		bit = bitmap_find_next_zero_area(msi->bitmap, INT_PCI_MSI_NR, 0,
>> +					 nr_irqs, nr_irqs - 1);
>> +	else
>> +		bit = bitmap_find_next_zero_area(msi->bitmap, INT_PCI_MSI_NR, 0,
>>  					 nr_irqs, 0);
>>  	if (bit >= INT_PCI_MSI_NR) {
>>  		mutex_unlock(&msi->lock);
>> -- 
>> 2.7.4
>>

This doesn't look like the best fix. The only case where nr_irqs is not 
set to 1 is when using Multi-MSI, so the '% 2' case actually covers all 
cases. Now, and in the interest of consistency, other drivers use a 
construct such as:

offset = bitmap_find_free_region(bitmap, bitmap_size,
				 get_count_order(nr_irqs));

which has the advantage of dealing with the bitmap setting as well.

I'd suggest something like this (completely untested):

diff --git a/drivers/pci/controller/pcie-xilinx-nwl.c b/drivers/pci/controller/pcie-xilinx-nwl.c
index 3b031f00a94a..8b9b58909e7c 100644
--- a/drivers/pci/controller/pcie-xilinx-nwl.c
+++ b/drivers/pci/controller/pcie-xilinx-nwl.c
@@ -482,15 +482,13 @@ static int nwl_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
 	int i;
 
 	mutex_lock(&msi->lock);
-	bit = bitmap_find_next_zero_area(msi->bitmap, INT_PCI_MSI_NR, 0,
-					 nr_irqs, 0);
-	if (bit >= INT_PCI_MSI_NR) {
+	bit = bitmap_find_free_region(msi->bitmap, INT_PCI_MSI_NR,
+				      get_count_order(nr_irqs));
+	if (bit < 0) {
 		mutex_unlock(&msi->lock);
 		return -ENOSPC;
 	}
 
-	bitmap_set(msi->bitmap, bit, nr_irqs);
-
 	for (i = 0; i < nr_irqs; i++) {
 		irq_domain_set_info(domain, virq + i, bit + i, &nwl_irq_chip,
 				domain->host_data, handle_simple_irq,
@@ -508,7 +506,7 @@ static void nwl_irq_domain_free(struct irq_domain *domain, unsigned int virq,
 	struct nwl_msi *msi = &pcie->msi;
 
 	mutex_lock(&msi->lock);
-	bitmap_clear(msi->bitmap, data->hwirq, nr_irqs);
+	bitmap_release_region(msi->bitmap, data->hwirq, get_count_order(nr_irqs));
 	mutex_unlock(&msi->lock);
 }
 

Thanks,

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