linux-kernel - Re: [PATCH 0/8] firewire: core/ohci: code refactoring for pages dedicated to DMA

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Message-ID: <20260112025506.GA245601@workstation.local>
Date: Mon, 12 Jan 2026 11:55:06 +0900
From: Takashi Sakamoto <o-takashi@...amocchi.jp>
To: linux1394-devel@...ts.sourceforge.net
Cc: linux-kernel@...r.kernel.org, jgg@...dia.com
Subject: Re: [PATCH 0/8] firewire: core/ohci: code refactoring for pages
 dedicated to DMA

On Sat, Jan 10, 2026 at 10:39:03AM +0900, Takashi Sakamoto wrote:
> Hi,
> 
> This patchset is to refactor current codes handling pages dedicated to
> DMA.
> 
> There are two cases to acquires pages dedicated to DMA; isochronous
> contexts and AR contexts. The reason of page acquisition is the need to map
> them into VMA. In the former case, they are mapped into userspace VMA. In
> the latter case, they are mapped into kernel VMA with continuous address
> to access to packet content across the page boundaries, especially between
> the end and the beginning of pages. The allocated pages are
> discontiguous, and their cache coherency is managed by DMA streaming
> APIs.
> 
> 1394 OHCI has no restriction about the size and alignment of memory
> registered for DMA, while the registered DMA address should be within
> 32 bit. The DMA mapped addresses can be discontiguous between descriptor,
> thus the above subsystem design is due to the convenience of system side.
> 
> I think the recent convention of driver programming relies on DMA-coherent
> buffers, while this code refactoring keeps the uses of DMA streaming
> APIs as is. Also, the acquisition per page is kept as is, even if there
> are some ways to allocate memories wider than the page size. They would be
> future works since it requires to change how to handle the packet content
> across the pages.
> 
> 
> Takashi Sakamoto (8):
>   firewire: core: move private function declaration from public header
>     to internal header
>   firewire: core: use mutex instead of spinlock for client isochronous
>     context
>   firewire: core: code refactoring with cleanup function for isoc pages
>   firewire: core: use common kernel API to allocate and release a batch
>     of pages
>   firewire: core: stop using page private to store DMA mapping address
>   firewire: ohci: use MAX macro to guarantee minimum count of pages for
>     AR contexts
>   firewire: ohci: split page allocation from dma mapping
>   firewire: ohci: stop using page private to store DMA mapping address
> 
>  drivers/firewire/core-cdev.c |  41 ++++++------
>  drivers/firewire/core-iso.c  |  86 +++++++++++++-----------
>  drivers/firewire/core.h      |   1 +
>  drivers/firewire/ohci.c      | 124 ++++++++++++++++++++---------------
>  include/linux/firewire.h     |   3 +-
>  5 files changed, 141 insertions(+), 114 deletions(-)

Applied to for-next branch.


Regards

Takashi Sakamoto