On 15.06.21 02:41, Marek Vasut wrote:
On 6/15/21 2:28 AM, Peng Fan (OSS) wrote:
On 2021/6/7 20:38, Marek Vasut wrote:
On 6/7/21 2:05 PM, Frieder Schrempf wrote:
From: Frieder Schrempf frieder.schrempf@kontron.de
Some IPs have their accessible address space restricted by the interconnect. Let's make sure U-Boot only ever uses the space below the 4G address boundary (which is 3GiB big), even when the effective available memory is bigger.
We implement board_get_usable_ram_top() for all i.MX8M SoCs, as the whole family is affected by this.
Shouldn't only those specific IP drivers handle buffers in the 64bit space somehow ? E.g. using a bounce buffer ?
That could cause extra mem copy.
If you want to avoid the extra memcopy, then make sure the buffers are not allocated above 4 GiB boundary. Then the bounce buffer does no copy.
This board_get_usable_ram_top() is just a temporary workaround for platforms with broken drivers which are not fixed yet, so please fix the drivers instead.
Bounce buffer would be good for systems that take U-Boot as UEFI firmware, because U-Boot would be located at high end, but in the middle just top of 4GB.
The bounce buffer is a necessity for IPs which cannot address more than the 4 GiB of memory. In fact, it would be even better to handle DT dma-ranges, but that is the next step.
I not object this patch, but it also be good if bounce buffer be added for improvement.
Reviewed-by: Peng Fan peng.fan@nxp.com
I do object to this, since it increases the proliferation of this broken board_get_usable_ram_top() workaround instead of fixing the drivers properly.
I generally agree with Marek's objections and if anyone comes up with a proper fix this will be highly appreciated. For now I just dropped this patch from my v2 patchset, but Stefano has already pulled it into u-boot-imx. I guess it's up to him to decide if this intermediate fix should be merged or not.