[PATCH v2] fastboot: scale default sparse max_download_size with available memory

[Sascha Hauer]

On Mon, Aug 28, 2023 at 10:17:55AM +0200, Ahmad Fatoum wrote:
> The fastboot host tool chokes when asked to sparse images that are not
> 4K-aligned:
> 
>   error: write_sparse_skip_chunk: don't care size 4280912 is not a multiple
>   of the block size 4096
> 
> This is often not a problem, because disk images tend to be 4K-aligned
> and are best converted to sparse images properly explicitly anyway, so
> don't care holes are preserved.
> 
> Bootloader binaries on the other hand are smaller than the default
> fastboot.max_download_size of 8M, so they are downloaded as a single
> chunk without problems.
> 
> Situation is different for kernel and FIT images, which aren't
> necessarily 4K aligned, usually bigger than 8M, and are usually
> compressed, so explicitly sparsing them doesn't save time and thus is
> usually not done.
> 
> Short of fixing the fastboot host tool, users can skip sparsing kernel
> images as well by choosing a suitable larger fastboot.max_download_size
> than the 8M default.
> 
> To improve user experience, let's scale max_download_size with the
> available memory. The minimum default value remains 8M, but the value
> can go up to 128M now and is computed by dividing available malloc
> area by 8 (roughly 1/16th of total SDRAM). For ARM systems, buffer
> sizes would now look like this:
> 
>   SDRAM Size	Fastboot Buffer size
> 
>   1024M		64M
>    512M		32M
>    256M		16M
>    128M		8M
> 
> To err on the side of caution, we only generate powers-of-two sizes.
> This only affects the default value and users can as before override
> it in the environment.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
> v1 -> v2:
>   - squash fixup fixing off by one in mem_malloc_size
>   - drop SZ_8M leftover in fastboot_max_download_size initialization.
>     It'll always be overridden anyway.
> ---
>  common/fastboot.c | 11 +++++++++--
>  include/memory.h  |  5 +++++
>  2 files changed, 14 insertions(+), 2 deletions(-)

Applied, thanks

Sascha

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