Message-ID: <CAMSpPPcC6wN+2HeZPak+gWxoy2WaO14epHNQfHT1W0FnTRHnOQ@mail.gmail.com>
Date:   Fri, 5 May 2017 00:11:19 +0530
From:   Oza Oza <oza.oza@...adcom.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Oza Pawandeep <oza.pawandeep@...il.com>
Subject: Re: [PATCH 1/3] of/pci/dma: fix DMA configuration for PCI masters

On Thu, May 4, 2017 at 11:32 PM, Robin Murphy <robin.murphy@....com> wrote:
> [apologies for the silence - I've been on holiday]
>
> On 03/05/17 05:46, Oza Pawandeep wrote:
>> current device framework and of framework integration assumes
>> dma-ranges in a way where memory-mapped devices define their
>> dma-ranges. (child-bus-address, parent-bus-address, length).
>
> Well, yes, that is simply the definition of dma-ranges, and remains true
> regardless of the particular format of either bus address.
>
>> of_dma_configure is specifically written to take care of memory
>> mapped devices. but no implementation exists for pci to take
>> care of pcie based memory ranges.
>
> That still doesn't make sense. To repeat myself again, PCI devices *ARE*
> memory-mapped devices. Yes, there do exist some platforms where I/O
> space is not treated as MMIO, but config space and memory space are very
> much memory-mapped however you look at them, and in the context of DMA,
> only memory space is relevant anyway.
>
> What *is* true about the current code is that of_dma_get_range() expects
> to be passed an OF node representing the device itself, and doesn't work
> properly when passed the node of the device's parent bus directly, which
> happens to be what pci_dma_configure() currently does. That's the only
> reason why it doesn't work for (single-entry) host controller dma-ranges
> today. This does not mean it's a PCI problem, it is simply the case that
> pci_dma_configure() is the only caller currently hitting it. Other
> discoverable, DMA-capable buses like fsl-mc are still going to face the
> exact same problem with or without this patch.
>
>> for e.g. iproc based SOCs and other SOCs(suc as rcar) have PCI
>> world dma-ranges.
>> dma-ranges = <0x43000000 0x00 0x00 0x00 0x00 0x80 0x00>;
>>
>> this patch serves following:
>>
>> 1) exposes interface to the pci host driver for their
>> inbound memory ranges
>>
>> 2) provide an interface to callers such as of_dma_get_ranges.
>> so then the returned size get best possible (largest) dma_mask.
>> because PCI RC drivers do not call APIs such as
>> dma_set_coherent_mask() and hence rather it shows its addressing
>> capabilities based on dma-ranges.
>> for e.g.
>> dma-ranges = <0x43000000 0x00 0x00 0x00 0x00 0x80 0x00>;
>> we should get dev->coherent_dma_mask=0x7fffffffff.
>>
>> 3) this patch handles multiple inbound windows and dma-ranges.
>> it is left to the caller, how it wants to use them.
>> the new function returns the resources in a standard and unform way
>>
>> 4) this way the callers of for e.g. of_dma_get_ranges
>> does not need to change.
>>
>> 5) leaves scope of adding PCI flag handling for inbound memory
>> by the new function.
>
> Which flags would ever actually matter? DMA windows aren't going to be
> to config or I/O space, so the memory type can be assumed, and the
> 32/64-bit distinction is irrelevant as it's not a relocatable BAR;
> DMA-able system memory isn't going to be read-sensitive, so the
> prefetchable flag shouldn't matter; and not being a BAR none of the
> others would be relevant either.
>

Thanks Robin; for your reply and attention:

agree with you, at present it would not matter,
but it does not mean that we do not scope it to make it matter in future.

now where it could matter:
there is Relaxed Ordering for inbound memory for PCI.
According to standard, Relaxed Ordering (RO) bit can be set only for
Memory requests and completions (if present in the original request).
Also, according to transaction ordering rules, I/O and configuration
requests can still be re-ordered ahead of each other.
and we would like to make use of it.
for e.g. lets say we mark memory as Relaxed Ordered with flag.
the special about this memory is incoming PCI transactions can be
reordered and rest memory has to be strongly ordered.

how it our SOC would make use of this is out of scope for the
discussion at this point of time, but I am just bringing in the
idea/point how flags could be useful
for inbound memory, since we would not like throw-away flags completely.

>>
>> Bug: SOC-5216
>> Change-Id: Ie045386df91e1e0587846bb147ae40d96f6d7d2e
>> Signed-off-by: Oza Pawandeep <oza.oza@...adcom.com>
>> Reviewed-on: http://gerrit-ccxsw.broadcom.net/40428
>> Reviewed-by: vpx_checkpatch status <vpx_checkpatch@...adcom.com>
>> Reviewed-by: CCXSW <ccxswbuild@...adcom.com>
>> Reviewed-by: Ray Jui <ray.jui@...adcom.com>
>> Tested-by: vpx_autobuild status <vpx_autobuild@...adcom.com>
>> Tested-by: vpx_smoketest status <vpx_smoketest@...adcom.com>
>> Tested-by: CCXSW <ccxswbuild@...adcom.com>
>> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
>>
>> diff --git a/drivers/of/of_pci.c b/drivers/of/of_pci.c
>> index 0ee42c3..ed6e69a 100644
>> --- a/drivers/of/of_pci.c
>> +++ b/drivers/of/of_pci.c
>> @@ -283,6 +283,83 @@ int of_pci_get_host_bridge_resources(struct device_node *dev,
>>       return err;
>>  }
>>  EXPORT_SYMBOL_GPL(of_pci_get_host_bridge_resources);
>> +
>> +/**
>> + * of_pci_get_dma_ranges - Parse PCI host bridge inbound resources from DT
>> + * @np: device node of the host bridge having the dma-ranges property
>> + * @resources: list where the range of resources will be added after DT parsing
>> + *
>> + * It is the caller's job to free the @resources list.
>> + *
>> + * This function will parse the "dma-ranges" property of a
>> + * PCI host bridge device node and setup the resource mapping based
>> + * on its content.
>> + *
>> + * It returns zero if the range parsing has been successful or a standard error
>> + * value if it failed.
>> + */
>> +
>> +int of_pci_get_dma_ranges(struct device_node *np, struct list_head *resources)
>> +{
>> +     struct device_node *node = of_node_get(np);
>> +     int rlen;
>> +     int ret = 0;
>> +     const int na = 3, ns = 2;
>> +     struct resource *res;
>> +     struct of_pci_range_parser parser;
>> +     struct of_pci_range range;
>> +
>> +     if (!node)
>> +             return -EINVAL;
>> +
>> +     parser.node = node;
>> +     parser.pna = of_n_addr_cells(node);
>> +     parser.np = parser.pna + na + ns;
>> +
>> +     parser.range = of_get_property(node, "dma-ranges", &rlen);
>> +
>> +     if (!parser.range) {
>> +             pr_debug("pcie device has no dma-ranges defined for node(%s)\n",
>> +                       np->full_name);
>> +             ret = -EINVAL;
>> +             goto out;
>> +     }
>> +
>> +     parser.end = parser.range + rlen / sizeof(__be32);
>> +
>> +     for_each_of_pci_range(&parser, &range) {
>
> This is plain wrong - of_pci_range_parser_one() will translate upwards
> through parent "ranges" properties, which is completely backwards for
> DMA addresses.
>
> Robin.
>

No it does not, this patch is thoroughly tested on our SOC and it works.
of_pci_range_parser_one does not translate upwards through parent. it
just sticks to given PCI parser.

>> +             /*
>> +              * If we failed translation or got a zero-sized region
>> +              * then skip this range
>> +              */
>> +             if (range.cpu_addr == OF_BAD_ADDR || range.size == 0)
>> +                     continue;
>> +
>> +             res = kzalloc(sizeof(struct resource), GFP_KERNEL);
>> +             if (!res) {
>> +                     ret = -ENOMEM;
>> +                     goto parse_failed;
>> +             }
>> +
>> +             ret = of_pci_range_to_resource(&range, np, res);
>> +             if (ret) {
>> +                     kfree(res);
>> +                     continue;
>> +             }
>> +
>> +             pci_add_resource_offset(resources, res,
>> +                                     res->start - range.pci_addr);
>> +     }
>> +
>> +     return ret;
>> +
>> +parse_failed:
>> +     pci_free_resource_list(resources);
>> +out:
>> +     of_node_put(node);
>> +     return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(of_pci_get_dma_ranges);
>>  #endif /* CONFIG_OF_ADDRESS */
>>
>>  #ifdef CONFIG_PCI_MSI
>> diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
>> index 0e0974e..617b90d 100644
>> --- a/include/linux/of_pci.h
>> +++ b/include/linux/of_pci.h
>> @@ -76,6 +76,7 @@ static inline void of_pci_check_probe_only(void) { }
>>  int of_pci_get_host_bridge_resources(struct device_node *dev,
>>                       unsigned char busno, unsigned char bus_max,
>>                       struct list_head *resources, resource_size_t *io_base);
>> +int of_pci_get_dma_ranges(struct device_node *np, struct list_head *resources);
>>  #else
>>  static inline int of_pci_get_host_bridge_resources(struct device_node *dev,
>>                       unsigned char busno, unsigned char bus_max,
>> @@ -83,6 +84,12 @@ static inline int of_pci_get_host_bridge_resources(struct device_node *dev,
>>  {
>>       return -EINVAL;
>>  }
>> +
>> +static inline int of_pci_get_dma_ranges(struct device_node *np,
>> +                                     struct list_head *resources)
>> +{
>> +     return -EINVAL;
>> +}
>>  #endif
>>
>>  #if defined(CONFIG_OF) && defined(CONFIG_PCI_MSI)
>>
>

I am posting v2, please have a look at it, it is very much improved
design, which address Rob's comments.

Regards,
Oza.

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