Hi Albert,
2015-07-13 15:51 GMT+09:00 Albert ARIBAUD albert.u.boot@aribaud.net:
Hello Masahiro,
On Mon, 13 Jul 2015 13:17:03 +0900, Masahiro Yamada yamada.masahiro@socionext.com wrote:
Please refer to the commit message of 06/14 for what this series wants to do.
Remark: you could use "Series-notes:" in 6/14 to have patman directly include said notes here instead of referring the reader to the patch.
Masahiro Yamada (14): x86: delete unneeded declarations of disable_irq() and enable_irq() linux_compat: remove cpu_relax() define linux_compat: move vzalloc() to header file as an inline function linux_compat: handle __GFP_ZERO in kmalloc() dm: add DM_FLAG_BOUND flag devres: introduce Devres (Managed Device Resource) framework devres: add devm_kmalloc() and friends (managed memory allocators) dm: refactor device_bind() and device_unbind() with devm_kzalloc() dm: merge fail_alloc labels linux_compat: introduce GFP_DMA flag for kmalloc() dm: refactor device_probe() and device_remove() with devm_kzalloc() devres: add debug command to dump device resources dm: remove redundant CONFIG_DM from driver/core/Makefile devres: compile Devres iif CONFIG_DM_DEVICE_REMOVE is enabled
I am still unsure why this is necessary. I had a discussion on the list with Simon, see last message here:
https://www.mail-archive.com/u-boot@lists.denx.de/msg177031.html
Unless I'm mistaken, the only case where we actually have a leak that this series would fix is in some cases of binding USB devices / drivers multiple times, and even then, it would take a considerable amount of repeated bindings before U-Boot could become unable to boot a payload; a scenario that I find unlikely.
I do understand the general goal of fixing bugs when we ind them; but I question the global benefit of fixing this specific leak bug by adding a whole new feature with a lot of code to U-Boot, as opposed to fixing it in a more ad hoc way with much less less code volume and complexity.
You have a point.
What we really want to avoid is to make low-level drivers too complicated by leaving the correct memory management to each of them.
After all, there turned out to be two options to solve it.
[1] Simon's driver model: move allocating/freeing memory to the driver core by having only the needed memory size specified in each driver [2] Devres: we still have to allocate memory in each driver, but we need not free it explicitly, making our driver work much easier
[1] and [2] are completely differently approach, but what they solve is the same: easier memory (resource) management without leak.
The only problem I see in [1] is that it is not controllable at run-time. The memory size for the auto-allocation must be specified at the compile time.
So, we need calloc() and free() in some low-level drivers. Simon might say they are only a few "exceptions", (my impression is I often hear the logic such as "it is not a problem because we do not have many.") Anyway, we had already lost the consistency as for memory allocation.
I imagined if [2] had been supported earlier, we would not have needed [1]. (at least, [2] seems more flexible to me.)
We already have many DM-based drivers, and I think we can live with [1] despite some exceptional drivers allocating memory on their own.
So, if Simon (and other developers) does not feel comfortable with this series, I do not mind discarding it.