Re: [PATCH] checkpatch: Add a --strict test for structs with bool member definitions

[yuankuiz]

Hi julia,

On 2018-04-15 05:19 AM, Julia Lawall wrote:
> On Wed, 11 Apr 2018, Joe Perches wrote:
>
> > On Thu, 2018-04-12 at 08:22 +0200, Julia Lawall wrote:
> > > On Wed, 11 Apr 2018, Joe Perches wrote:
> > > > On Wed, 2018-04-11 at 09:29 -0700, Andrew Morton wrote:
> > > > > We already have some 500 bools-in-structs
> > > >
> > > > I got at least triple that only in include/
> > > > so I expect there are at probably an order
> > > > of magnitude more than 500 in the kernel.
> > > >
> > > > I suppose some cocci script could count the
> > > > actual number of instances.  A regex can not.
> > >
> > > I got 12667.
> >
> > Could you please post the cocci script?
> >
> > > I'm not sure to understand the issue.  Will using a bitfield help if there
> > > are no other bitfields in the structure?
> >
> > IMO, not really.
> >
> > The primary issue is described by Linus here:
> > https://lkml.org/lkml/2017/11/21/384
> >
> > I personally do not find a significant issue with
> > uncontrolled sizes of bool in kernel structs as
> > all of the kernel structs are transitory and not
> > written out to storage.
> >
> > I suppose bool bitfields are also OK, but for the
> > RMW required.
> >
> > Using unsigned int :1 bitfield instead of bool :1
> > has the negative of truncation so that the uint
> > has to be set with !! instead of a simple assign.
>
> At least with gcc 5.4.0, a number of structures become larger with
> unsigned int :1. bool:1 seems to mostly solve this problem.  The 
> structure
> ichx_desc, defined in drivers/gpio/gpio-ich.c seems to become larger 
> with
> both approaches.
[ZJ] Hopefully, this could make it better in your environment.
     IMHO, this is just for double check.

diff --git a/drivers/gpio/gpio-ich.c b/drivers/gpio/gpio-ich.c
index 4f6d643..b46e170 100644
--- a/drivers/gpio/gpio-ich.c
+++ b/drivers/gpio/gpio-ich.c
@@ -70,6 +70,18 @@ static const u8 avoton_reglen[3] = {
 #define ICHX_READ(reg, base_res)       inl((reg) + (base_res)->start)

 struct ichx_desc {
+       /* GPO_BLINK is available on this chipset */
+       bool uses_gpe0:1;
+
+       /* Whether the chipset has GPIO in GPE0_STS in the PM IO region 
*/
+        bool uses_gpe0:1;
+
+        /*
+         * Some chipsets don't let reading output values on GPIO_LVL 
register
+         * this option allows driver caching written output values
+         */
+        bool use_outlvl_cache:1;
+
        /* Max GPIO pins the chipset can have */
        uint ngpio;

@@ -77,24 +89,12 @@ struct ichx_desc {
        const u8 (*regs)[3];
        const u8 *reglen;

-       /* GPO_BLINK is available on this chipset */
-       bool have_blink;
-
-       /* Whether the chipset has GPIO in GPE0_STS in the PM IO region 
*/
-       bool uses_gpe0;
-
        /* USE_SEL is bogus on some chipsets, eg 3100 */
        u32 use_sel_ignore[3];

        /* Some chipsets have quirks, let these use their own 
request/get */
        int (*request)(struct gpio_chip *chip, unsigned offset);
        int (*get)(struct gpio_chip *chip, unsigned offset);
-
-       /*
-        * Some chipsets don't let reading output values on GPIO_LVL 
register
-        * this option allows driver caching written output values
-        */
-       bool use_outlvl_cache;
 };


ZJ