Re: [PATCH] kconfig: Minimize 'Selected by' and 'Implied by'

[Eugeniu Rosca <roscaeugeniu@gmail.com>]

Hello Petr,

On Sun, Feb 04, 2018 at 04:50:54PM +0100, Petr Vorel wrote:
> Hi Eugeniu,
> 
> > From: Eugeniu Rosca <erosca@de.adit-jv.com>
> 
> > 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@de.adit-jv.com>
> > ---
> >  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);
> 
> Thanks for trying to improve my change.
> 
> Applying your patch, running
> $ ARCH=arm64 make defconfig && ARCH=arm64 make menuconfig
> and searching for USB prints "Selected by:" with nothing actually selected.

I think the behavior is correct. All expressions that select USB
translate/evaluate to =n. CONFIG_USB is enabled in the arm64 defconfig.

> Kind regards,
> Petr

Thanks,
Eugeniu.