lkml.org 
[lkml]   [2017]   [Jan]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH V6 1/5] LIB: Indirect ISA/LPC port IO introduced
From
Date


On 31/01/2017 14:32, John Garry wrote:
> On 30/01/2017 17:12, Alexander Graf wrote:
>> On 01/24/2017 08:05 AM, zhichang.yuan wrote:
>>> Low-pin-count interface is integrated into some SoCs. The accesses to
>>> those
>>> peripherals under LPC make use of I/O ports rather than the memory
>>> mapped I/O.
>>>
>>> To drive these devices, this patch introduces a method named
>>> indirect-IO.
>>> In this method the in/out() accessor in include/asm-generic/io.h will be
>>> redefined. When upper layer drivers call in/out() with those known
>>> legacy port
>>> addresses to access the peripherals, the I/O operations will be routed
>>> to the
>>> right hooks which are registered specific to the host device, such as
>>> LPC.
>>> Then the hardware relevant manupulations are finished by the
>>> corresponding
>>> host.
>>>
>>> According to the comments on V5, this patch adds a common indirect-IO
>>> driver
>>> which support this I/O indirection to the generic directory.
>>>
>>> In the later pathches, some host-relevant drivers are implemented to
>>> support
>>> the specific I/O hooks and register them.
>>> Based on these, the upper layer drivers which depend on in/out() can
>>> work well
>>> without any extra work or any changes.
>>>
>>> Signed-off-by: zhichang.yuan <yuanzhichang@hisilicon.com>
>>> Signed-off-by: Gabriele Paoloni <gabriele.paoloni@huawei.com>
>>> Signed-off-by: John Garry <john.garry@huawei.com>
>>
>> I like the extio idea. That allows us to handle all PIO requests on
>> platforms that don't have native PIO support via different routes
>> depending on the region they're in. Unfortunately we now we have 2
>> frameworks for handling sparse PIO regions: One in extio, one in PCI.
>>
>> Why don't we just merge the two? Most of the code that has #ifdef
>> PCI_IOBASE throughout the code base sounds like an ideal candidate to
>> get migrated to extio instead. Then we only have a single framework to
>> worry about ...
>
> To be clear, are you suggesting we merge the functionality from
> pci_register_io_range(), pci_pio_to_address(), pci_address_to_pio() into
> extio, so extio manages all PIO?

Yes, I guess so.

> And having a single type of node to
> register PIO ranges, by amalgamating struct extio_node and io_range (as
> Bjorn mentioned)?

I'm not quite sure I follow you here. Basically I think you want a
generic "non-x86 PIO" framework that PCI just plugs into.

I don't think that necessarily means you want to statically allocate
regions of that PIO space to separate (pseudo-)devices. Instead,
everyone shares that space and should be able to fail gracefully if some
space is already occupied.

> It would make sense. We would be somewhat decoupling PIO from PCI.

Yes :).

> I think that other architectures, like PPC, and other code would need to
> be fixed up to handle this.

I think only PPC, Microblaze and ARM are using this. Grep for
PCI_IOBASE. It's not that many.

> We need to consider all the other challenges/obstacles to this.

Well, getting our abstraction levels right to me sounds like it's worth
the obstacles.

>
>>
>>> ---
>>> include/asm-generic/io.h | 50 ++++++++++++++++
>>> include/linux/extio.h | 85 +++++++++++++++++++++++++++
>>> include/linux/io.h | 1 +
>>> lib/Kconfig | 8 +++
>>> lib/Makefile | 2 +
>>> lib/extio.c | 147
>>> +++++++++++++++++++++++++++++++++++++++++++++++ xc>> create mode
>>> 100644 include/linux/extio.h
>>> create mode 100644 lib/extio.c
>>>
>
> <snip>
>
>>> + * Copyright (C) 2016 Hisilicon Limited, All Rights Reserved.
>>> + * Author: Zhichang Yuan <yuanzhichang@hisilicon.com>
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License version 2 as
>>> + * published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * You should have received a copy of the GNU General Public License
>>> + * along with this program. If not, see
>>> <http://www.gnu.org/licenses/>.
>>> + */
>>> +
>>> +#include <linux/io.h>
>>> +#include <linux/spinlock.h>
>>> +
>>> +static LIST_HEAD(extio_dev_list);
>>> +static DEFINE_RWLOCK(extio_list_lock);
>>
>> Why not just make the list an RCU list? Then you don't need read locks.
>> We also wouldn't create potential lock contention between devices that
>> could easily have parallel PIO operations (say a PCI device and an LPC
>> device).
>>
>
> OK
>
>>> +
>>> +void register_extio(struct extio_node *node)
>>> +{
>>> + write_lock(&extio_list_lock);
>>> + list_add_tail(&node->list, &extio_dev_list);
>>> + write_unlock(&extio_list_lock);
>>> +}
>>> +
>>> +static struct extio_node *find_extio_token(unsigned long addr)
>>> +{
>>> + struct extio_node *extio_entry;
>>> +
>>> + read_lock(&extio_list_lock);
>>> + list_for_each_entry(extio_entry, &extio_dev_list, list) {
>>> + if ((addr < extio_entry->io_start + extio_entry->range_size) &&
>>> + (addr >= extio_entry->io_start))
>>> + break;
>>> + }
>>> + read_unlock(&extio_list_lock);
>>> + return (&extio_entry->list == &extio_dev_list) ? NULL :
>>> extio_entry;
>>> +}
>>> +
>>> +struct extio_node *extio_find_node(struct fwnode_handle *node)
>>> +{
>>> + struct extio_node *entry;
>>> +
>>> + read_lock(&extio_list_lock);
>>> + list_for_each_entry(entry, &extio_dev_list, list) {
>>> + if (entry->fwnode == node)
>>> + break;
>>> + }
>>> + read_unlock(&extio_list_lock);
>>> +
>>> + return (&entry->list == &extio_dev_list) ? NULL : entry;
>>> +}
>>> +
>>> +unsigned long extio_translate(struct fwnode_handle *node,
>>> + unsigned long bus_addr)
>>> +{
>>> + struct extio_node *entry;
>>> + unsigned long port_id = -1;
>>> +
>>> + read_lock(&extio_list_lock);
>>> + list_for_each_entry(entry, &extio_dev_list, list) {
>>> + if (entry->fwnode == node &&
>>> + bus_addr >= entry->bus_start &&
>>> + bus_addr - entry->bus_start < entry->range_size)
>>> + port_id = entry->io_start + bus_addr -
>>> + entry->bus_start;
>>> + }
>>> + read_unlock(&extio_list_lock);
>>> +
>>> + return port_id;
>>> +}
>>> +
>>> +#ifdef PCI_IOBASE
>>> +
>>> +#define BUILD_EXTIO(bw, type) \
>>> +type extio_in##bw(unsigned long addr) \
>>> +{ \
>>> + struct extio_node *extio_entry = find_extio_token(addr); \
>>> + \
>>> + if (!extio_entry) \
>>> + return read##bw(PCI_IOBASE + addr); \
>>> + return extio_entry->ops->pfin ? \
>>> + extio_entry->ops->pfin(extio_entry->devpara, \
>>> + addr, sizeof(type)) : -1; \
>>> +} \
>>> + \
>>> +void extio_out##bw(type value, unsigned long addr) \
>>> +{ \
>>> + struct extio_node *extio_entry = find_extio_token(addr); \
>>> + \
>>> + if (!extio_entry) \
>>> + write##bw(value, PCI_IOBASE + addr); \
>>
>> All of the fallback code would also disappear as a nice side effect of
>> making pci pio handling a user of extio :).
>
> Is your idea that PCI IO space will also register accessors, which would
> be the same read{b,w,l}/write{b,w,l}?

Yes. If you need to later on accelerate that bit, you can always do
something like

if (extio_entry->ops->pfin == pci_extio_in)
return pci_extio_in(...);

which should get you all the prefetcher and branch prediction benefits
that the current version gives you. But for starters I'd leave that out,
since I doubt it'll have measurable performance impact to go via an
indirect function call.

>
>>
>
> It would be nice to have a quicker way to so the lookup from address to
> node, as we loop all nodes in find_extio_token() every single time.

You can always replace the search with a tree. But to me that's an
implementation detail that's easy enough to replace in a follow-up patch
series.


Alex

\
 
 \ /
  Last update: 2017-01-31 20:38    [W:0.072 / U:1.420 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site