Hi Simon,
On 16/8/20 00:06, Simon Glass wrote:
Hi Walter,
On Sun, 26 Jul 2020 at 20:45, Walter Lozano walter.lozano@collabora.com wrote:
Hi Simon,
On 10/7/20 01:12, Walter Lozano wrote:
Hi Simon,
On 2/7/20 18:10, Simon Glass wrote:
This series provides a proposed enhancement to driver model to reduce overhead in SPL.
These patches should not be reviewed other than to comment on the approach. The code is all lumped together in a few patches and so cannot be applied as is.
For now, the source tree is available at:
https://gitlab.denx.de/u-boot/custodians/u-boot-dm/-/tree/dtoc-working
Comments welcome!
Benefits (good news)
As an example of the impact of tiny-dm, chromebook_jerry is converted to use it. This shows approximately a 30% reduction in code and data size and a 85% reduction in malloc() space over of-platdata:
text data bss dec hex filename 25248 1836 12 27096 69d8 spl/u-boot-spl(original with DT) 19727 3436 12 23175 5a87 spl/u-boot-spl (OF_PLATDATA) 78% 187% 100% 86% as %age of original
13784 1408 12 15204 3b64 spl/u-boot-spl(SPL_TINY) 70% 41% 100% 66% as %age of platdata 55% 77% 100% 56% as %age of original
SPL malloc() usage drops from 944 bytes (OF_PLATDATA) to 116 (SPL_TINY).
Overall the 'overhead' of tiny-dm is much less than the full driver model. Code size is currently about 600 bytes for these functions on Thumb2:
00000054 T tiny_dev_probe 00000034 T tiny_dev_get_by_drvdata 00000024 T tiny_dev_find 0000001a T tiny_dev_get 0000003c T tinydev_alloc_data 0000002a t tinydev_lookup_data 00000022 T tinydev_ensure_data 00000014 T tinydev_get_data 00000004 T tinydev_get_parentEffort (bad news)
Unfortunately it is quite a bit of work to convert drivers over to tiny-dm. First, the of-platdata conversion must be done. But on top of that, tiny-dm needs entirely separate code for dealing with devices. This means that instead of 'struct udevice' and 'struct uclass' there is just 'struct tinydev'. Each driver and uclass must be modified to support both, pulling common code into internal static functions.
Another option
Note: It is assumed that any board that is space-contrained should use of-platdata in SPL (see doc/driver-model/of-plat.rst). This is shown to reduce device-tree overhead by approximately 4KB.
Designing tiny-dm has suggested a number of things that could be changed in the current driver model to make it more space-efficient for TPL and SPL. The ones with least impact on driver code are (CS=reduces code size, DS=reduces data size):
CS - drop driver_bind() and create devices (struct udevice) at build-time CS - allocate all device- and uclass-private data at build-time CS - remove all but the basic operations for each uclass (e.g. SPI flash only supports reading) DS - use 8-bit indexes instead of 32/64-bit pointers for device pointers possible since these are created at build-time) DS - use singly-linked lists DS - use 16-bit offsets to private data, instead of 32/64-bitpointers (possible since it is all in SRAM relative to malloc() base, presumably word-aligned and < 256KB) DS - move private pointers into a separate data structure so that NULLs are not stored CS / DS - Combine req_seq and seq and calculate the new value at build-time
More difficult are:
DS - drop some of the lesser-used driver and uclass methods DS - drop all uclass methods except init() DS - drop all driver methods except probe() CS / DS - drop uclasses and require drivers to manually call uclass functionsEven with all of this we would not reach tiny-dm and it would muddy up the driver-model datas structures. But we might come close to tiny-dm on size and there are some advantages:
- much of the benefit would apply to all boards that use of-platdata
(i.e. with very little effort on behalf of board maintainers)
- the impact on the code base is much less (we keep a single, unified driver mode in SPL and U-Boot proper)
Overall I think it is worth looking at this option. While it doesn't have the 'nuclear' impact of tiny-dm, neither does it mess with the U-Boot driver code as much and it is easier to learn.
Thanks for your hard work on this topic.
I think that there is great value in this research and in this conclusion. It is clear that there two different approaches, but I feel that the improvement to the current DM implementation would have a higher impact in the community.
Since the first version of this proposal I have been thinking in a solution that takes some of the advantages of tiny-dm idea but that does not require so much effort. This seems to be aligned with what you have been explaining in this section.
I found interesting your proposal about simplification some data structures. In this sense one of my ideas, a bit biased by some of the improvements in dtoc, is to change the the definition of struct driver based on if OF_PLATDATA is enabled, and in this case remove some properties.
struct driver { #if !CONFIG_IS_ENABLED(OF_PLATDATA) char *name; #endif enum uclass_id id; #if !CONFIG_IS_ENABLED(OF_PLATDATA) const struct udevice_id *of_match; #endif int (*bind)(struct udevice *dev); int (*probe)(struct udevice *dev); int (*remove)(struct udevice *dev); int (*unbind)(struct udevice *dev); int (*ofdata_to_platdata)(struct udevice *dev); int (*child_post_bind)(struct udevice *dev); int (*child_pre_probe)(struct udevice *dev); int (*child_post_remove)(struct udevice *dev); int priv_auto_alloc_size; int platdata_auto_alloc_size; int per_child_auto_alloc_size; int per_child_platdata_auto_alloc_size; const void *ops; /* driver-specific operations */ uint32_t flags; #if CONFIG_IS_ENABLED(ACPIGEN) struct acpi_ops *acpi_ops; #endif };
By just removing those properties, we save some bytes as we get rid of several strings. Also maybe it would be nice to add some macros to make it cleaner in drivers to use or not those properties, instead of adding lots of #if.
I feel, as you clearly expressed, that some additional refactotring can be made to make the logic be more similar to the tiny-dm one. I also found interesting that several of your proposals will have impact in U-Boot, not only in TPL/SPL.
Just to be a bit more clear, I was thinking in something like
diff --git a/include/dm/device.h b/include/dm/device.h index f5738a0cee..0ee239be8f 100644 --- a/include/dm/device.h +++ b/include/dm/device.h @@ -203,6 +203,16 @@ struct udevice_id { #define of_match_ptr(_ptr) NULL #endif /* CONFIG_IS_ENABLED(OF_CONTROL) */
+#if !CONFIG_IS_ENABLED(OF_PLATDATA) +#undef OF_PLATDATA_TINY +#define STRUCT_FIELD(x) x; +#define STRUCT_VALUE(x) x, +#else +#define OF_PLATDATA_TINY +#define STRUCT_FIELD(x) +#define STRUCT_VALUE(x) +#endif
- /**
- struct driver - A driver for a feature or peripheral
@@ -252,9 +262,9 @@ struct udevice_id { * allowing the device to add things to the ACPI tables passed to Linux */ struct driver {
char *name;
STRUCT_FIELD(char *name) enum uclass_id id;
const struct udevice_id *of_match;
STRUCT_FIELD(const struct udevice_id *of_match)I didn't actually reply to this, but I think this makes sense. Perhaps have a DM_ prefix on your #defines? (
Thanks for your reply and paying attention to my comments. I totally agree that if you implement this idea you should rename #defines to make them more readable.
int (*bind)(struct udevice *dev); int (*probe)(struct udevice *dev); int (*remove)(struct udevice *dev);diff --git a/drivers/core/simple-bus.c b/drivers/core/simple-bus.c index 7cc1d46009..e303d59daf 100644 --- a/drivers/core/simple-bus.c +++ b/drivers/core/simple-bus.c @@ -57,8 +57,8 @@ static const struct udevice_id generic_simple_bus_ids[] = { };
U_BOOT_DRIVER(simple_bus) = {
.name = "simple_bus",
STRUCT_VALUE(.name = "simple_bus") .id = UCLASS_SIMPLE_BUS,
.of_match = generic_simple_bus_ids,
STRUCT_VALUE(.of_match = generic_simple_bus_ids) .flags = DM_FLAG_PRE_RELOC,Please don't pay attention to how OF_PLATDATA_TINY is implemented, it is just part of the test. I think it should be a configuration option that removes some functionality from OF_PLATDATA, like having the overhead of the strings. On top of this you could add additional improvements, like the binding implementation in tiny-dm which uses DM_REF_TINY_DRIVER.
Yes OK. I am thinking of starting with just adding a parent. But time is not my friend at present so it will probably be a month or so.
Thanks for sharing your plans. Time is always an issue, but I think we are in the right track, and that all the research you have done with tiny-dm will give great benefits.
Regards,
Walter