Re: [PATCH v8 20/45] powerpc/powernv: Allocate PE# in reverse order
From: Alexey Kardashevskiy <hidden>
Date: 2016-04-19 03:07:59
Also in:
linux-devicetree, linux-pci
On 02/17/2016 02:44 PM, Gavin Shan wrote:
PE number for one particular PE can be allocated dynamically or reserved according to the consumed M64 (64-bits prefetchable) segments of the PE. The M64 resources, and hence their segments and PE number are assigned/reserved in ascending order. The PE numbers are allocated dynamically in ascending order as well. It's not a problem as the PE numbers are reserved and then allocated all at once in fine order. However, it will introduce conflicts when PCI hotplug is supported: the PE number to be reserved for newly added PE might have been assigned. To resolve above conflicts, this forces the PE number to be allocated dynamically in reverse order. With this patch applied, the PE numbers are reserved in ascending order, but allocated dynamically in reverse order.
The patch is probably is ok, the commit log is not - I do not follow it. Some PEs are reserved (for what? why does the absolute PE number matter? put it in the commit log), that means that the corresponding bits in pe_alloc[] should be set so when you will be allocating PEs for a just plugged device, you won't pick them and you will pick free ones, and the order should not matter. I would think that "reservation" happens once at the boot time so you set "used" bits for the reserved PEs then and after that the dynamic allocator will skip them.
quoted hunk ↗ jump to hunk
Signed-off-by: Gavin Shan <redacted> --- arch/powerpc/platforms/powernv/pci-ioda.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c index f182ca7..565725b 100644 --- a/arch/powerpc/platforms/powernv/pci-ioda.c +++ b/arch/powerpc/platforms/powernv/pci-ioda.c@@ -144,16 +144,14 @@ static void pnv_ioda_reserve_pe(struct pnv_phb *phb, int pe_no) static struct pnv_ioda_pe *pnv_ioda_alloc_pe(struct pnv_phb *phb) { - unsigned long pe; + unsigned long pe = phb->ioda.total_pe_num - 1; - do { - pe = find_next_zero_bit(phb->ioda.pe_alloc, - phb->ioda.total_pe_num, 0); - if (pe >= phb->ioda.total_pe_num) - return NULL; - } while(test_and_set_bit(pe, phb->ioda.pe_alloc)); + for (pe = phb->ioda.total_pe_num - 1; pe >= 0; pe--) { + if (!test_and_set_bit(pe, phb->ioda.pe_alloc)) + return pnv_ioda_init_pe(phb, pe); + } - return pnv_ioda_init_pe(phb, pe); + return NULL; } static void pnv_ioda_free_pe(struct pnv_ioda_pe *pe)
-- Alexey