Re: [PATCH 2.6.20 1/1] fbdev,mm: hecuba/E-Ink fbdev driver

From: Jaya Kumar
Date: Wed Feb 21 2007 - 11:46:40 EST

On 2/20/07, Jaya Kumar <jayakumar.lkml@xxxxxxxxx> wrote:
On 2/19/07, Paul Mundt <lethal@xxxxxxxxxxxx> wrote:
> That works for me, though I'd prefer for struct page_list to be done with
> a scatterlist, then it's trivial to setup from the workqueue context
> without having to shuffle things around.

Ok. Will check out when implementing.

Took a quick look. If I used scatterlist, I'd still need to build a
list of scatterlist to pass to the driver callback. The alternative
being a preallocated array of scatterlist based on the page count of
the framebuffer, which seems expensive since scatterlist has page,
offset, dma and length.

On a separate note, Peter pointed out that it may be possible to reuse
page->lru instead of using a struct page_list. This would enable
something like:

in mkwrite:
list_add(page->lru, defio->pagelist)

in deferred handler:
for_each page {
callback(fb_info, pagelist)
for_each page {

The advantage of reusing page->lru is that avoids needing the struct
page_list and allocation in mkwrite. Is the above exploitation of
->lru ok with mm folk?

In above, we're iterating over the page list twice. I have to mkclean
before calling the callback to avoid the situation where a touched
page is missed by the callback. I don't see a way around that part.

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