Re: [PATCH] PCI: endpoint: Migrate to Genalloc framework for outbound window memory allocation

From: Frank Li
Date: Wed Mar 20 2024 - 10:27:02 EST

On Wed, Mar 20, 2024 at 11:40:34AM +0530, Manivannan Sadhasivam wrote:
> On Tue, Mar 19, 2024 at 01:01:03PM -0400, Frank Li wrote:
> > On Tue, Mar 19, 2024 at 09:58:29PM +0530, Manivannan Sadhasivam wrote:
> > > On Tue, Mar 19, 2024 at 11:50:50AM -0400, Frank Li wrote:
> > > > On Sun, Mar 17, 2024 at 11:39:17AM +0530, Manivannan Sadhasivam wrote:
> > > > > As proposed during the last year 'PCI Endpoint Subsystem Open Items
> > > > > Discussion' of Linux Plumbers conference [1], let's migrate to Genalloc
> > > > > framework for managing the endpoint outbound window memory allocation.
> > > > >
> > > > > PCI Endpoint subsystem is using a custom memory allocator in pci-epc-mem
> > > > > driver from the start for managing the memory required to map the host
> > > > > address space (outbound) in endpoint. Even though it works well, it
> > > > > completely defeats the purpose of the 'Genalloc framework', a general
> > > > > purpose memory allocator framework created to avoid various custom memory
> > > > > allocators in the kernel.
> > > > >
> > > > > The migration to Genalloc framework is done is such a way that the existing
> > > > > API semantics are preserved. So that the callers of the EPC mem APIs do not
> > > > > need any modification (apart from the pcie-designware-epc driver that
> > > > > queries page size).
> > > > >
> > > > > Internally, the EPC mem driver now uses Genalloc framework's
> > > > > 'gen_pool_first_fit_order_align' algorithm that aligns the allocated memory
> > > > > based on the requested size as like the previous allocator. And the
> > > > > page size passed during pci_epc_mem_init() API is used as the minimum order
> > > > > for the memory allocations.
> > > > >
> > > > > During the migration, 'struct pci_epc_mem' is removed as it is seems
> > > > > redundant and the existing 'struct pci_epc_mem_window' in 'struct pci_epc'
> > > > > is now used to hold the address windows of the endpoint controller.
> > > > >
> > > > > [1] https://lpc.events/event/17/contributions/1419/
> > > > >
> > > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> > > > > ---
> > > > > drivers/pci/controller/dwc/pcie-designware-ep.c | 14 +-
> > > > > drivers/pci/endpoint/pci-epc-mem.c | 182 +++++++++---------------
> > > > > include/linux/pci-epc.h | 25 +---
> > > > > 3 files changed, 81 insertions(+), 140 deletions(-)
> > > > >
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > > index 5befed2dc02b..37c612282eb6 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > > @@ -482,11 +482,11 @@ int dw_pcie_ep_raise_msi_irq(struct dw_pcie_ep *ep, u8 func_no,
> > > > > reg = ep_func->msi_cap + PCI_MSI_DATA_32;
> > > > > msg_data = dw_pcie_ep_readw_dbi(ep, func_no, reg);
> > > > > }
> > > > > - aligned_offset = msg_addr_lower & (epc->mem->window.page_size - 1);
> > > > > + aligned_offset = msg_addr_lower & (epc->windows[0]->page_size - 1);
> > > > > msg_addr = ((u64)msg_addr_upper) << 32 |
> > > > > (msg_addr_lower & ~aligned_offset);
> > > > > ret = dw_pcie_ep_map_addr(epc, func_no, 0, ep->msi_mem_phys, msg_addr,
> > > > > - epc->mem->window.page_size);
> > > > > + epc->windows[0]->page_size);
> > > > > if (ret)
> > > > > return ret;
> > > > >
> > > > > @@ -550,10 +550,10 @@ int dw_pcie_ep_raise_msix_irq(struct dw_pcie_ep *ep, u8 func_no,
> > > > > return -EPERM;
> > > > > }
> > > > >
> > > > > - aligned_offset = msg_addr & (epc->mem->window.page_size - 1);
> > > > > + aligned_offset = msg_addr & (epc->windows[0]->page_size - 1);
> > > > > msg_addr &= ~aligned_offset;
> > > > > ret = dw_pcie_ep_map_addr(epc, func_no, 0, ep->msi_mem_phys, msg_addr,
> > > > > - epc->mem->window.page_size);
> > > > > + epc->windows[0]->page_size);
> > > > > if (ret)
> > > > > return ret;
> > > > >
> > > > > @@ -572,7 +572,7 @@ void dw_pcie_ep_exit(struct dw_pcie_ep *ep)
> > > > > dw_pcie_edma_remove(pci);
> > > > >
> > > > > pci_epc_mem_free_addr(epc, ep->msi_mem_phys, ep->msi_mem,
> > > > > - epc->mem->window.page_size);
> > > > > + epc->windows[0]->page_size);
> > > > >
> > > > > pci_epc_mem_exit(epc);
> > > > >
> > > > > @@ -742,7 +742,7 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> > > > > }
> > > > >
> > > > > ep->msi_mem = pci_epc_mem_alloc_addr(epc, &ep->msi_mem_phys,
> > > > > - epc->mem->window.page_size);
> > > > > + epc->windows[0]->page_size);
> > > > > if (!ep->msi_mem) {
> > > > > ret = -ENOMEM;
> > > > > dev_err(dev, "Failed to reserve memory for MSI/MSI-X\n");
> > > > > @@ -770,7 +770,7 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> > > > >
> > > > > err_free_epc_mem:
> > > > > pci_epc_mem_free_addr(epc, ep->msi_mem_phys, ep->msi_mem,
> > > > > - epc->mem->window.page_size);
> > > > > + epc->windows[0]->page_size);
> > > > >
> > > > > err_exit_epc_mem:
> > > > > pci_epc_mem_exit(epc);
> > > > > diff --git a/drivers/pci/endpoint/pci-epc-mem.c b/drivers/pci/endpoint/pci-epc-mem.c
> > > > > index a9c028f58da1..f9e6e1a6aeaa 100644
> > > > > --- a/drivers/pci/endpoint/pci-epc-mem.c
> > > > > +++ b/drivers/pci/endpoint/pci-epc-mem.c
> > > > > @@ -4,37 +4,18 @@
> > > > > *
> > > > > * Copyright (C) 2017 Texas Instruments
> > > > > * Author: Kishon Vijay Abraham I <kishon@xxxxxx>
> > > > > + *
> > > > > + * Copyright (C) 2024 Linaro Ltd.
> > > > > + * Author: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> > > > > */
> > > > >
> > > > > +#include <linux/genalloc.h>
> > > > > #include <linux/io.h>
> > > > > #include <linux/module.h>
> > > > > #include <linux/slab.h>
> > > > >
> > > > > #include <linux/pci-epc.h>
> > > > >
> > > > > -/**
> > > > > - * pci_epc_mem_get_order() - determine the allocation order of a memory size
> > > > > - * @mem: address space of the endpoint controller
> > > > > - * @size: the size for which to get the order
> > > > > - *
> > > > > - * Reimplement get_order() for mem->page_size since the generic get_order
> > > > > - * always gets order with a constant PAGE_SIZE.
> > > > > - */
> > > > > -static int pci_epc_mem_get_order(struct pci_epc_mem *mem, size_t size)
> > > > > -{
> > > > > - int order;
> > > > > - unsigned int page_shift = ilog2(mem->window.page_size);
> > > > > -
> > > > > - size--;
> > > > > - size >>= page_shift;
> > > > > -#if BITS_PER_LONG == 32
> > > > > - order = fls(size);
> > > > > -#else
> > > > > - order = fls64(size);
> > > > > -#endif
> > > > > - return order;
> > > > > -}
> > > > > -
> > > > > /**
> > > > > * pci_epc_multi_mem_init() - initialize the pci_epc_mem structure
> > > > > * @epc: the EPC device that invoked pci_epc_mem_init
> > > > > @@ -48,17 +29,11 @@ int pci_epc_multi_mem_init(struct pci_epc *epc,
> > > > > struct pci_epc_mem_window *windows,
> > > > > unsigned int num_windows)
> > > > > {
> > > > > - struct pci_epc_mem *mem = NULL;
> > > > > - unsigned long *bitmap = NULL;
> > > > > - unsigned int page_shift;
> > > > > + struct pci_epc_mem_window *window = NULL;
> > > > > size_t page_size;
> > > > > - int bitmap_size;
> > > > > - int pages;
> > > > > int ret;
> > > > > int i;
> > > > >
> > > > > - epc->num_windows = 0;
> > > > > -
> > > > > if (!windows || !num_windows)
> > > > > return -EINVAL;
> > > > >
> > > > > @@ -70,45 +45,51 @@ int pci_epc_multi_mem_init(struct pci_epc *epc,
> > > > > page_size = windows[i].page_size;
> > > > > if (page_size < PAGE_SIZE)
> > > > > page_size = PAGE_SIZE;
> > > > > - page_shift = ilog2(page_size);
> > > > > - pages = windows[i].size >> page_shift;
> > > > > - bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);
> > > > >
> > > > > - mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> > > > > - if (!mem) {
> > > > > + windows[i].pool = gen_pool_create(ilog2(page_size), -1);
> > > >
> > > > I think it is not good to modify caller's memory. This funciton suppose
> > > > pass down read-only information. And set to epc->windows[i]. I think it'd
> > > > better to use epc->windows[i].pool/windows.
> > > >
> > >
> > > What do you mean by modifying caller's memory? Here, the memory for epc->windows
> > > is being allocated and the pool is created for each window.
> >
> > windows[i].pool = gen_pool_create(ilog2(page_size), -1)
> >
> > 'windows' pass down from argument pci_epc_multi_mem_init(
> > ..struct pci_epc_mem_window *windows, )
> > ^^^^^^^
> > windows[i].pool = gen_pool_create() actually change the caller's stack
> > memory.
> >
>
> Hmm, you are right. Will fix it.
>
> > >
> > > > > + if (!windows[i].pool) {
> > > > > ret = -ENOMEM;
> > > > > - i--;
> > > > > - goto err_mem;
> > > > > + goto err_free_mem;
> > > > > + }
> > > > > +
> > > > > + gen_pool_set_algo(windows[i].pool, gen_pool_first_fit_order_align,
> > > > > + NULL);
> > > > > +
> > > > > + windows[i].virt_base = ioremap(windows[i].phys_base, windows[i].size);
> > > > > + ret = gen_pool_add_virt(windows[i].pool, (unsigned long)windows[i].virt_base,
> > > > > + windows[i].phys_base, windows[i].size, -1);
> > > > > + if (ret) {
> > > > > + iounmap(windows[i].virt_base);
> > > > > + gen_pool_destroy(epc->windows[i]->pool);
> > > >
> > > > I think move all free to err path will be easy to understand.
> > > >
> > >
> > > It is not straightforward. First we need to free the memory for current
> > > iteration and then all previous iterations, that too from different places.
> > > Moving the code to free current iteration to the error label will look messy.
> >
> > All from current iteration.
> >
> > err_free_mem:
> > iounmap(windows[i].virt_base);
> > if (epc->windows[i]->pool)
> > gen_pool_destroy(epc->windows[i]->pool)
>
> Initially I thought it would look messy if the memory for current iteration is
> freed in the error labels. But now I implemented it and it doesn't look that
> bad. So will change it in next iteration.
>
> >
> > >
> > > > > + goto err_free_mem;
> > > > > }
> > > > >
> > > > > - bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> > > > > - if (!bitmap) {
> > > > > + window = kzalloc(sizeof(*window), GFP_KERNEL);
> > > >
> > > > According to below code
> > > >
> > > > epc->windows = kcalloc(num_windows, sizeof(*epc->windows), GFP_KERNEL);
> > > > if (!epc->windows)
> > > > return -ENOMEM;
> > > >
> > > > epc->windows already allocate whole num_windows * "struct pci_epc_mem_window".
> > > > I think you can direct use 'window = epc->windows + i', so needn't alloc
> > > > additional memory for epc->windows[i].
> > > >
> > >
> > > First we are allocating the memory for 'struct pci_epc_mem_window' _pointers_ in
> > > epc->windows. Then we need to allocate memory for each pointer in epc->windows
> > > to actually store data. Otherwise, we will be referencing the nulll pointer.
> >
> > I think two layer pointer is totally unecessary.
> > You can use one layer pointer 'struct pci_epc_mem_window *windows;'
> >
>
> How can you store multiple 'struct pci_epc_mem_window' with a single pointer?
> Please elaborate.

struct pci_epc
{
...
struct pci_epc_mem_window *windows;
...
}

pci_epc_multi_mem_init(struct pci_epc *epc,
struct pci_epc_mem_window *windows,
unsigned int num_windows)
{
...
epc->windows = kcalloc(num_windows, sizeof(*epc->windows), GFP_KERNEL);
...

for (i = 0; i < num_windows; i++) {

struct pci_epc_mem_window *win = epc->windows + i;

*win = windows[i]; //copy everthing from 'windows' to EPC

win->pool = gen_pool_create(ilog2(page_size), -1);
...
win->page_size = PAGE_SIZE;

//below code also can be removed
//+ window->phys_base = windows[i].phys_base;
//+ window->size = windows[i].size;
//+ window->page_size = page_size;
//+ window->pool = windows[i].pool;
//+ epc->windows[i] = window;

}
}

Frank

>
> - Mani
>
> --
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