Re: [PATCH v9 09/12] PCI: brcmstb: Set additional internal memory DMA viewport sizes

Nicolas Saenz Julienne
2020-08-01T17:39:42Z

Hi Jim,

On Fri, 2020-07-24 at 16:33 -0400, Jim Quinlan wrote:
> The Raspberry Pi (RPI) is currently the only chip using this driver
> (pcie-brcmstb.c). There, only one memory controller is used, without an
> extension region, and the SCB0 viewport size is set to the size of the
> first and only dma-range region. Other BrcmSTB SOCs have more complicated
> memory configurations that require setting additional viewport sizes.
>
> BrcmSTB PCIe controllers are intimately connected to the memory
> controller(s) on the SOC. The SOC may have one to three memory
> controllers; they are indicated by the term SCBi. Each controller has a
> base region and an optional extension region. In physical memory, the base
> and extension regions of a controller are not adjacent, but in PCIe-space
> they are.
>
> There is a "viewport" for each memory controller that allows DMA from
> endpoint devices. Each viewport's size must be set to a power of two, and
> that size must be equal to or larger than the amount of memory each
> controller supports which is the sum of base region and its optional
> extension. Further, the 1-3 viewports are also adjacent in PCIe-space.
>
> Unfortunately the viewport sizes cannot be ascertained from the
> "dma-ranges" property so they have their own property, "brcm,scb-sizes".
> This is because dma-range information does not indicate what memory
> controller it is associated. For example, consider the following case
> where the size of one dma-range is 2GB and the second dma-range is 1GB:
>
> /* Case 1: SCB0 size set to 4GB */
> dma-range0: 2GB (from memc0-base)
> dma-range1: 1GB (from memc0-extension)
>
> /* Case 2: SCB0 size set to 2GB, SCB1 size set to 1GB */
> dma-range0: 2GB (from memc0-base)
> dma-range1: 1GB (from memc0-extension)
>
> By just looking at the dma-ranges information, one cannot tell which
> situation applies. That is why an additional property is needed. Its
> length indicates the number of memory controllers being used and each value
> indicates the viewport size.
>
> Note that the RPI DT does not have a "brcm,scb-sizes" property value,
> as it is assumed that it only requires one memory controller and no
> extension. So the optional use of "brcm,scb-sizes" will be backwards
> compatible.
>
> One last layer of complexity exists: all of the viewports sizes must be
> added and rounded up to a power of two to determine what the "BAR" size is.
> Further, an offset must be given that indicates the base PCIe address of
> this "BAR". The use of the term BAR is typically associated with endpoint
> devices, and the term is used here because the PCIe HW may be used as an RC
> or an EP. In the former case, all of the system memory appears in a single
> "BAR" region in PCIe memory. As it turns out, BrcmSTB PCIe HW is rarely
> used in the EP role and its system of mapping memory is an artifact that
> requires multiple dma-ranges regions.
>
> Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
> drivers/pci/controller/pcie-brcmstb.c | 68 ++++++++++++++++++++-------
> 1 file changed, 50 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> index 8dacb9d3b7b6..3ef2d37cc43b 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -715,22 +720,44 @@ static inline int brcm_pcie_get_rc_bar2_size_and_offset(struct brcm_pcie *pcie,
> u64 *rc_bar2_offset)
> {
> struct pci_host_bridge *bridge = pci_host_bridge_from_priv(pcie);
> - struct device *dev = pcie->dev;
> struct resource_entry *entry;
> + struct device *dev = pcie->dev;
> + u64 lowest_pcie_addr = ~(u64)0;
> + int ret, i = 0;
> + u64 size = 0;
>
> - entry = resource_list_first_type(&bridge->dma_ranges, IORESOURCE_MEM);
> - if (!entry)
> - return -ENODEV;
> + resource_list_for_each_entry(entry, &bridge->dma_ranges) {
> + u64 pcie_beg = entry->res->start - entry->offset;
>
> + size += entry->res->end - entry->res->start + 1;
> + if (pcie_beg < lowest_pcie_addr)
> + lowest_pcie_addr = pcie_beg;
> + }
>
> - /*
> - * The controller expects the inbound window offset to be calculated as
> - * the difference between PCIe's address space and CPU's. The offset
> - * provided by the firmware is calculated the opposite way, so we
> - * negate it.
> - */
> - *rc_bar2_offset = -entry->offset;
> - *rc_bar2_size = 1ULL << fls64(entry->res->end - entry->res->start);
> + if (lowest_pcie_addr == ~(u64)0) {
> + dev_err(dev, "DT node has no dma-ranges\n");
> + return -EINVAL;
> + }
> +
> + ret = of_property_read_variable_u64_array(pcie->np, "brcm,scb-sizes", pcie->memc_size, 1,
> + PCIE_BRCM_MAX_MEMC);
> +
> + if (ret <= 0) {
> + /* Make an educated guess */
> + pcie->num_memc = 1;
> + pcie->memc_size[0] = 1 << fls64(size - 1);

You need to 1ULL here.

Regards,
Nicolas

> + } else {
> + pcie->num_memc = ret;
> + }
> +
> + /* Each memc is viewed through a "port" that is a power of 2 */
> + for (i = 0, size = 0; i < pcie->num_memc; i++)
> + size += pcie->memc_size[i];
> +
> + /* System memory starts at this address in PCIe-space */
> + *rc_bar2_offset = lowest_pcie_addr;
> + /* The sum of all memc views must also be a power of 2 */
> + *rc_bar2_size = 1ULL << fls64(size - 1);
>
> /*
> * We validate the inbound memory view even though we should trust