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

[Kishon Vijay Abraham I <kvijayab@amd.com>]

On 4/18/2024 10:54 AM, Manivannan Sadhasivam wrote:
> On Thu, Apr 18, 2024 at 10:14:57AM +0530, Kishon Vijay Abraham I wrote:
>> Hi Mani,
>>
>> On 4/14/2024 6:30 PM, Manivannan Sadhasivam wrote:
>>> On Wed, Mar 20, 2024 at 04:59:28PM +0530, Manivannan Sadhasivam wrote:
>>>> On Wed, Mar 20, 2024 at 03:26:41PM +0530, Kishon Vijay Abraham I wrote:
>>>>> Hi Mani,
>>>>>
>>>>> On 3/17/2024 11:39 AM, 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/
>>>>>
>>>>> Thank you for working on this!
>>>>>>
>>>>>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>>>>>> ---
>>>>>>     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/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@ti.com>
>>>>>> + *
>>>>>> + * Copyright (C) 2024 Linaro Ltd.
>>>>>> + * Author: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>>>>>>      */
>>>>>> +#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);
>>>>>> +		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);
>>>>>
>>>>> Do you have to ioremap upfront the entire window? This could be a problem in
>>>>> 32-bit systems which has limited vmalloc space. I have faced issues before
>>>>> when trying to map the entire memory window and had to manipulate vmalloc
>>>>> boot parameter.
>>>>>
>>>>> I'd prefer we find a way to do ioremap per allocation as before.
>>>>>
>>>>
>>>> Hmm, thanks for pointing it out. Current genalloc implementation works on the
>>>> virtual address as opposed to physical address (that might be due to majority of
>>>> its users managing the virtual address only). That's the reason I did ioremap of
>>>> the entire window upfront.
>>>>
>>>> Let me see if we can somehow avoid this.
>>>>
>>>
>>> Looks like we have to introduce some good amount of change to support dynamic
>>> ioremap with genalloc. But IMO it doesn't worth the effort to introduce these
>>> changes for some old systems which are supposed to go away soon.
>>>
>>> So I think we can keep the old and genalloc based allocators and use the old one
>>> only for 32bit systems and genalloc allocator for the rest.
>>>
>>> What do you think?
>>
>> sure, that should be okay. But can we check with genalloc maintainers to see
>> what they think?
>>
> 
> There seems to be no maintainer for genalloc. It was written way back in 2005
> and improved by lot of folks. But there is no one to take care of it.

Ah ok :-/ We'll keep both for now as you suggested then.

Thanks,
Kishon