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Date: Wed, 20 Apr 2016 20:16:37 +0200
From: Eric Auger <eric.auger@...aro.org>
To: Marc Zyngier <marc.zyngier@....com>
Cc: eric.auger@...com, robin.murphy@....com,
alex.williamson@...hat.com, will.deacon@....com, joro@...tes.org,
tglx@...utronix.de, jason@...edaemon.net,
christoffer.dall@...aro.org, linux-arm-kernel@...ts.infradead.org,
patches@...aro.org, linux-kernel@...r.kernel.org,
Bharat.Bhushan@...escale.com, pranav.sawargaonkar@...il.com,
p.fedin@...sung.com, iommu@...ts.linux-foundation.org,
Jean-Philippe.Brucker@....com, julien.grall@....com
Subject: Re: [PATCH v7 6/8] irqchip/gicv2m: implement msi_doorbell_info
callback
Marc,
On 04/20/2016 07:56 PM, Marc Zyngier wrote:
> On Wed, 20 Apr 2016 14:33:17 +0200
> Eric Auger <eric.auger@...aro.org> wrote:
>
>> Marc,
>> On 04/20/2016 11:27 AM, Marc Zyngier wrote:
>>> On 19/04/16 18:13, Eric Auger wrote:
>>>> This patch implements the msi_doorbell_info callback in the
>>>> gicv2m driver.
>>>>
>>>> The driver now is able to return its doorbell characteristics
>>>> (base, size, prot). A single doorbell is exposed.
>>>>
>>>> This will allow the msi layer to iommu_map this doorbell when
>>>> requested.
>>>>
>>>> Signed-off-by: Eric Auger <eric.auger@...aro.org>
>>>>
>>>> ---
>>>>
>>>> v7: creation
>>>> ---
>>>> drivers/irqchip/irq-gic-v2m.c | 32 +++++++++++++++++++++++++++++++-
>>>> 1 file changed, 31 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/irqchip/irq-gic-v2m.c b/drivers/irqchip/irq-gic-v2m.c
>>>> index 28f047c..54690b9 100644
>>>> --- a/drivers/irqchip/irq-gic-v2m.c
>>>> +++ b/drivers/irqchip/irq-gic-v2m.c
>>>> @@ -24,6 +24,8 @@
>>>> #include <linux/of_pci.h>
>>>> #include <linux/slab.h>
>>>> #include <linux/spinlock.h>
>>>> +#include <linux/percpu.h>
>>>> +#include <linux/iommu.h>
>>>>
>>>> /*
>>>> * MSI_TYPER:
>>>> @@ -64,6 +66,7 @@ struct v2m_data {
>>>> u32 nr_spis; /* The number of SPIs for MSIs */
>>>> unsigned long *bm; /* MSI vector bitmap */
>>>> u32 flags; /* v2m flags for specific implementation */
>>>> + struct irq_chip_msi_doorbell_info doorbell_info;
>>>> };
>>>>
>>>> static void gicv2m_mask_msi_irq(struct irq_data *d)
>>>> @@ -105,6 +108,16 @@ static void gicv2m_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>>>> msg->data -= v2m->spi_start;
>>>> }
>>>>
>>>> +static const struct irq_chip_msi_doorbell_info *
>>>> +gicv2m_msi_doorbell_info(struct irq_data *data)
>>>> +{
>>>> + struct v2m_data *v2m = irq_data_get_irq_chip_data(data);
>>>> +
>>>> + if (!v2m)
>>>> + return NULL;
>>>
>>> How can this ever be NULL? I think you can drop that test.
>> OK
>>>
>>>> + return (const struct irq_chip_msi_doorbell_info *)(&v2m->doorbell_info);
>>>
>>> Please don't do that. Use "const" in the functions that are using
>>> irq_chip_msi_doorbell_info, but do not make this "const" here.
>> It definitively compiles without casting so obviously this is not needed
>> but is there any other wrong thing I don't see?
>> we still want this function to return a pointer to a const?
>
> I don't think we can return a const pointer, because it is obviously
> not (the memory has been kmalloc'ed, and you've written to it, so it is
> not really "read-only").
I see what you are afraid of now and I will remove it; will ask some
compiler guys ;-)
Have a nice evening
Eric
>
> Maybe I'm being overly zealous, but I've seen compilers taking amazing
> shortcuts when offered a const qualifier...
>
>>>
>>>> +}
>>>> +
>>>> static struct irq_chip gicv2m_irq_chip = {
>>>> .name = "GICv2m",
>>>> .irq_mask = irq_chip_mask_parent,
>>>> @@ -112,6 +125,7 @@ static struct irq_chip gicv2m_irq_chip = {
>>>> .irq_eoi = irq_chip_eoi_parent,
>>>> .irq_set_affinity = irq_chip_set_affinity_parent,
>>>> .irq_compose_msi_msg = gicv2m_compose_msi_msg,
>>>> + .msi_doorbell_info = gicv2m_msi_doorbell_info,
>>>> };
>>>>
>>>> static int gicv2m_irq_gic_domain_alloc(struct irq_domain *domain,
>>>> @@ -247,6 +261,7 @@ static void gicv2m_teardown(void)
>>>>
>>>> list_for_each_entry_safe(v2m, tmp, &v2m_nodes, entry) {
>>>> list_del(&v2m->entry);
>>>> + free_percpu(v2m->doorbell_info.percpu_doorbells);
>>>> kfree(v2m->bm);
>>>> iounmap(v2m->base);
>>>> of_node_put(to_of_node(v2m->fwnode));
>>>> @@ -299,6 +314,7 @@ static int __init gicv2m_init_one(struct fwnode_handle *fwnode,
>>>> {
>>>> int ret;
>>>> struct v2m_data *v2m;
>>>> + struct irq_chip_msi_doorbell __percpu *doorbell;
>>>>
>>>> v2m = kzalloc(sizeof(struct v2m_data), GFP_KERNEL);
>>>> if (!v2m) {
>>>> @@ -311,11 +327,23 @@ static int __init gicv2m_init_one(struct fwnode_handle *fwnode,
>>>>
>>>> memcpy(&v2m->res, res, sizeof(struct resource));
>>>>
>>>> + v2m->doorbell_info.percpu_doorbells =
>>>> + alloc_percpu(struct irq_chip_msi_doorbell);
>>>> + if (WARN_ON(!v2m->doorbell_info.percpu_doorbells)) {
>>>> + ret = -ENOMEM;
>>>> + goto err_free_v2m;
>>>> + }
>>>> + doorbell = per_cpu_ptr(v2m->doorbell_info.percpu_doorbells, 0);
>>>> + doorbell->base = v2m->res.start;
>>>> + doorbell->size = 4;
>>>> + doorbell->prot = IOMMU_WRITE;
>>>
>>> You probably need to also have something that says IOMMU_DEVICE or
>>> something similar, because I'm afraid you're getting a memory mapping
>>> here. I've had a quick look at the two other series, but couldn't find
>>> anything that would force the memory attributes.
>> Yes you're right I currently just enforce the direction (which is
>> checked against what VFIO user registered). Do you refer to IOMMU_MMIO,
>> latterly proposed on the ML. In the positive, yes I intend to add it
>> once it gets upstreamed.
>
> Yeah, Robin's patches should become a dependency here, because there is
> absolutely no guarantee that the device write to the doorbell won't be
> treated a normal cacheable memory, with disastrous effects.
>
> Thanks,
>
> M.
>
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