On Sun, Feb 4, 2018 at 3:46 PM, Ulf Magnusson <ulfalizer@xxxxxxxxx> wrote:
> On Sun, Feb 4, 2018 at 12:37 PM, Eugeniu Rosca <roscaeugeniu@xxxxxxxxx> wrote:
>> From: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
>>
>> Commit 1ccb27143360 ("kconfig: make "Selected by:" and "Implied by:"
>> readable") made an incredible improvement in how reverse dependencies
>> are perceived by the user, by breaking down the single (often
>> interminable) expression string into small readable chunks.
>>
>> Even so, what happens in practice when reading the reverse
>> dependencies is that 80-90% of the OR sub-expressions simply don't
>> matter, since they evaluate to [=n].
>>
>> Assuming commit 617aebe6a97e ("Merge tag 'usercopy-v4.16-rc1' of
>> git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux"), ARCH=arm64
>> and vanilla arm64 defconfig, here is the top 30 of CONFIG options with
>> the highest amount of OR sub-expressions that make up the final
>> "{Selected,Implied} by" reverse dependency expression.
>>
>> | Config | Revdep all | Revdep ![=n] |
>> |-------------------------------|------------|--------------|
>> | REGMAP_I2C | 212 | 9 |
>> | CRC32 | 167 | 25 |
>> | FW_LOADER | 128 | 5 |
>> | MFD_CORE | 124 | 9 |
>> | FB_CFB_IMAGEBLIT | 114 | 2 |
>> | FB_CFB_COPYAREA | 111 | 2 |
>> | FB_CFB_FILLRECT | 110 | 2 |
>> | SND_PCM | 103 | 2 |
>> | CRYPTO_HASH | 87 | 19 |
>> | WATCHDOG_CORE | 86 | 6 |
>> | IRQ_DOMAIN | 75 | 19 |
>> | SERIAL_CORE | 75 | 9 |
>> | PHYLIB | 74 | 16 |
>> | REGMAP_MMIO | 72 | 15 |
>> | GENERIC_PHY | 67 | 20 |
>> | DMA_ENGINE | 66 | 11 |
>> | SERIAL_CORE_CONSOLE | 64 | 9 |
>> | CRYPTO_BLKCIPHER | 64 | 13 |
>> | PINMUX | 60 | 17 |
>> | CRYPTO | 59 | 10 |
>> | MII | 58 | 8 |
>> | GPIOLIB_IRQCHIP | 58 | 9 |
>> | MFD_SYSCON | 58 | 15 |
>> | VIDEOBUF2_DMA_CONTIG | 46 | 4 |
>> | REGMAP_IRQ | 45 | 6 |
>> | REGMAP_SPI | 44 | 2 |
>> | CLKSRC_MMIO | 42 | 5 |
>> | SND_SOC_GENERIC_DMAENGINE_PCM | 41 | 3 |
>> | CRYPTO_SHA1 | 37 | 2 |
>> | REGMAP | 36 | 4 |
>>
>> The story behind the above is that we still need to visually
>> review/evaluate 212 expressions which *potentially* select REGMAP_I2C
>> in order to identify the expressions which *actually* select
>> REGMAP_I2C, for a particular ARCH and for a particular defconfig used.
>>
>> This patch attempts to bring at user's fingertips those reverse
>> dependencies that actually participate in selection of given symbol
>> filtering out the rest of them.
>>
>> Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
>> ---
>> scripts/kconfig/expr.c | 24 +++++++++++++++++-------
>> 1 file changed, 17 insertions(+), 7 deletions(-)
>>
>> diff --git a/scripts/kconfig/expr.c b/scripts/kconfig/expr.c
>> index 2ba332b3fed7..147b2d8a8f3e 100644
>> --- a/scripts/kconfig/expr.c
>> +++ b/scripts/kconfig/expr.c
>> @@ -1234,14 +1234,24 @@ static void __expr_print(struct expr *e, void (*fn)(void *, struct symbol *, con
>> fn(data, e->right.sym, e->right.sym->name);
>> break;
>> case E_OR:
>> - if (revdep && e->left.expr->type != E_OR)
>> - fn(data, NULL, "\n - ");
>> - __expr_print(e->left.expr, fn, data, E_OR, revdep);
>> - if (revdep)
>> - fn(data, NULL, "\n - ");
>> - else
>> + if (revdep) {
>> + struct expr *left = e->left.expr;
>> + struct expr *right = e->right.expr;
>> +
>> + if (expr_calc_value(left) != no) {
>> + if (left->type != E_OR)
>> + fn(data, NULL, "\n - ");
>> + __expr_print(left, fn, data, E_OR, revdep);
>> + }
>> + if (expr_calc_value(right) != no) {
>> + fn(data, NULL, "\n - ");
>> + __expr_print(right, fn, data, E_OR, revdep);
>> + }
>> + } else {
>> + __expr_print(e->left.expr, fn, data, E_OR, revdep);
>> fn(data, NULL, " || ");
>> - __expr_print(e->right.expr, fn, data, E_OR, revdep);
>> + __expr_print(e->right.expr, fn, data, E_OR, revdep);
>> + }
>> break;
>> case E_AND:
>> expr_print(e->left.expr, fn, data, E_AND);
>> --
>> 2.16.1
>>
>
> Hello,
>
> One downside to this is that people might expect e.g. the '?'
> menuconfig screen to list all the selecting symbols and use it as a
> reference.
>
> The best solution IMO would be to have a separate "Currently selected
> by:" section on that screen, listing just the non-n selects. The
> simpler next best thing would be to just replace the "Selected by:"
> heading with "Currently selected by:", to make it clear that it
> includes just the active selects.
>
> For the most-selected symbols you listed, most of them end up as "m"
> on my system by the way, because they come from drivers compiled in as
> modules.
Most of the selecting symbols that is.
> "n" is the minority. Might want to check that most of the
> ones with a million selects aren't like that, because it might not be
> that hard to see what's going on for those anyway.
>
> I used a similar approach in
> https://github.com/ulfalizer/Kconfiglib/blob/master/kconfiglib.py#L3022
> by the way. I was always a bit worried that all the expression
> simplification shenanigans going on in the C implementation might mess
> with an approach like that, but it seems fine in practice. :)
>
> Cheers,
> Ulf
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