Re: [PATCH] firmware: cs_dsp: Fix fragmentation regression in firmware download

[Takashi Iwai <tiwai@suse.de>]

On Wed, 04 Mar 2026 15:12:50 +0100,
Richard Fitzgerald wrote:
> 
> Use vmalloc() instead of kmalloc(..., GFP_DMA) to alloc the temporary
> buffer for firmware download blobs. This avoids the problem that a
> heavily fragmented system cannot allocate enough physically-contiguous
> memory for a large blob.
> 
> The redundant alloc buffer mechanism was removed in commit 900baa6e7bb0
> ("firmware: cs_dsp: Remove redundant download buffer allocator").
> While doing that I was overly focused on the possibility of the
> underlying bus requiring DMA-safe memory. So I used GFP_DMA kmalloc()s.
> I failed to notice that the code I was removing used vmalloc().
> This creates a regression.
> 
> Way back in 2014 the problem of fragmentation with kmalloc()s was fixed
> by commit cdcd7f728753 ("ASoC: wm_adsp: Use vmalloc to allocate firmware
> download buffer").
> 
> Although we don't need physically-contiguous memory, we don't know if the
> bus needs some particular alignment of the buffers. Since the change in
> 2014, the firmware download has always used whatever alignment vmalloc()
> returns. To avoid introducing a new problem, the temporary buffer is still
> used, to keep the same alignment of pointers passed to regmap_raw_write().
> 
> Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
> Fixes: 900baa6e7bb0 ("firmware: cs_dsp: Remove redundant download buffer allocator")

FYI, if the data isn't always large, kvmalloc() could be a better
alternative, which is a hybrid for both speed and size, too.


Takashi