Re: [PATCH] platform/x86:dell-laptop: Add knobs to change battery charge settings

Pali Rohár
2024-07-20T09:55:12Z

On Saturday 20 July 2024 05:24:19 Andres Salomon wrote:
> Thanks for the quick feedback! Responses below.
>
> On Sat, 20 Jul 2024 10:40:19 +0200
> Pali Rohár <pali@kernel.org> wrote:
>
> > Hello,
> >
> > I looked at your patch. I wrote some comments below. The main issue is
> > how to correctly interpret read token values.
> >
> [...]
>
> >
> > dell_send_request() returns negative value on error. As the read value
> > seems to be always non-negative number, you can change API of the
> > dell_battery_read_req() function to have read value in the return value
> > (instead of in *val pointer). E.g.
> >
> > static int dell_battery_read_req(const int type)
> > {
> > ...
> > err = dell_send_request(&buffer, CLASS_TOKEN_READ, SELECT_TOKEN_STD);
> > if (err)
> > return err;
> >
> > return buffer.output[1];
> > }
> >
>
> Good call, I'll change that.
>
>
> > > +
> > > +static int dell_battery_write_req(const int type, int val)
> > > +{
> > > + struct calling_interface_buffer buffer;
> > > + struct calling_interface_token *token;
> > > +
> > > + token = dell_smbios_find_token(type);
> > > + if (!token)
> > > + return -ENODEV;
> > > +
> > > + dell_fill_request(&buffer, token->location, val, 0, 0);
> > > + return dell_send_request(&buffer,
> > > + CLASS_TOKEN_WRITE, SELECT_TOKEN_STD);
> > > +}
> > > +
> > > +/* The rules: the minimum start charging value is 50%. The maximum
> > > + * start charging value is 95%. The minimum end charging value is
> > > + * 55%. The maximum end charging value is 100%. And finally, there
> > > + * has to be at least a 5% difference between start & end values.
> > > + */
> > > +#define CHARGE_START_MIN 50
> > > +#define CHARGE_START_MAX 95
> > > +#define CHARGE_END_MIN 55
> > > +#define CHARGE_END_MAX 100
> > > +#define CHARGE_MIN_DIFF 5
> > > +
> > > +static int dell_battery_custom_set(const int type, int val)
> > > +{
> > > + if (type == BAT_CUSTOM_CHARGE_START) {
> > > + int end = CHARGE_END_MAX;
> > > +
> > > + if (val < CHARGE_START_MIN)
> > > + val = CHARGE_START_MIN;
> > > + else if (val > CHARGE_START_MAX)
> > > + val = CHARGE_START_MAX;
> > > +
> > > + dell_battery_read_req(BAT_CUSTOM_CHARGE_END, &end);
> >
> > Missing check for failure of dell_battery_read_req.
>
> This is intentional; it's just a sanity check, we don't need to bail
> if we hit a failure. I'll change the code to make that explicit
> though, as it's not currently clear.
>
>
>
> >
> > > + if ((end - val) < CHARGE_MIN_DIFF)
> > > + val = end - CHARGE_MIN_DIFF;
> > > + } else if (type == BAT_CUSTOM_CHARGE_END) {
> > > + int start = CHARGE_START_MIN;
> > > +
> > > + if (val < CHARGE_END_MIN)
> > > + val = CHARGE_END_MIN;
> > > + else if (val > CHARGE_END_MAX)
> > > + val = CHARGE_END_MAX;
> > > +
> > > + dell_battery_read_req(BAT_CUSTOM_CHARGE_START, &start);
> >
> > Missing check for failure of dell_battery_read_req.
> >
>
> Ditto.
>
>
> > > + if ((val - start) < CHARGE_MIN_DIFF)
> > > + val = start + CHARGE_MIN_DIFF;
> > > + }
> > > +
> > > + return dell_battery_write_req(type, val);
> > > +}
> > > +
> > > +static int battery_charging_mode_set(enum battery_charging_mode mode)
> > > +{
> > > + int err;
> > > +
> > > + switch (mode) {
> > > + case DELL_BAT_MODE_STANDARD:
> > > + err = dell_battery_write_req(BAT_STANDARD_MODE_TOKEN, mode);
> > > + break;
> > > + case DELL_BAT_MODE_EXPRESS:
> > > + err = dell_battery_write_req(BAT_EXPRESS_MODE_TOKEN, mode);
> > > + break;
> > > + case DELL_BAT_MODE_PRIMARILY_AC:
> > > + err = dell_battery_write_req(BAT_PRI_AC_MODE_TOKEN, mode);
> > > + break;
> > > + case DELL_BAT_MODE_ADAPTIVE:
> > > + err = dell_battery_write_req(BAT_ADAPTIVE_MODE_TOKEN, mode);
> > > + break;
> > > + case DELL_BAT_MODE_CUSTOM:
> > > + err = dell_battery_write_req(BAT_CUSTOM_MODE_TOKEN, mode);
> > > + break;
> > > + default:
> > > + err = -EINVAL;
> > > + }
> > > +
> > > + return err;
> > > +}
> >
> > You can make whole function smaller by avoiding err variable:
> >
> > static int battery_charging_mode_set(enum battery_charging_mode mode)
> > {
> > switch (mode) {
> > case DELL_BAT_MODE_STANDARD:
> > return dell_battery_write_req(BAT_STANDARD_MODE_TOKEN, mode);
> > case DELL_BAT_MODE_EXPRESS:
> > return dell_battery_write_req(BAT_EXPRESS_MODE_TOKEN, mode);
> > case DELL_BAT_MODE_PRIMARILY_AC:
> > return dell_battery_write_req(BAT_PRI_AC_MODE_TOKEN, mode);
> > case DELL_BAT_MODE_ADAPTIVE:
> > return dell_battery_write_req(BAT_ADAPTIVE_MODE_TOKEN, mode);
> > case DELL_BAT_MODE_CUSTOM:
> > return dell_battery_write_req(BAT_CUSTOM_MODE_TOKEN, mode);
> > default:
> > return -EINVAL;
> > }
> > }
> >
>
> Okay, I'll change it.
>
>
> > > +
> > > +static ssize_t charge_type_show(struct device *dev,
> > > + struct device_attribute *attr,
> > > + char *buf)
> > > +{
> > > + enum battery_charging_mode mode;
> > > + ssize_t count = 0;
> > > +
> > > + for (mode = DELL_BAT_MODE_STANDARD; mode < DELL_BAT_MODE_MAX; mode++) {
> > > + if (battery_state[mode]) {
> > > + count += sysfs_emit_at(buf, count,
> > > + mode == bat_chg_current ? "[%s] " : "%s ",
> > > + battery_state[mode]);
> > > + }
> > > + }
> > > +
> > > + /* convert the last space to a newline */
> > > + count--;
> > > + count += sysfs_emit_at(buf, count, "\n");
> >
> > Here is missing protection in the case when number of valid modes is
> > zero, so count is 0 and buf was untouched.
> >
>
> This will never be zero (based on the hardcoded value of DELL_BAT_MODE_MAX),

Now I see. You are iterating over members of constant array battery_state[].
I overlooked it and I thought that this iteration over mode values.

What about writing the for- conditions to be visible that you are
iterating over the array? E.g.

size_t i;
...
for (i = 0; i < ARRAY_SIZE(battery_state); i++) {
if (!battery_state[i])
continue;
count += sysfs_emit_at(buf, count, i == bat_chg_current ? "[%s] " : "%s ", battery_state[i]);
}
...

This has an advantage that you do not depend on DELL_BAT_MODE_MAX value,
compiler will calculate upper bound automatically.

Or another way. You can define array of tokens, like it is done for
keyboard backlight. See how the array kbd_tokens[] is used.

With this approach you can completely get rid of the DELL_BAT_MODE_MAX.

> but perhaps a static_assert or BUILD_BUG_ON to verify that the number of
> modes > 0?

I think it is not needed.

>
> > > +
> > > + return count;
> > > +}
> > > +
> > > +static ssize_t charge_type_store(struct device *dev,
> > > + struct device_attribute *attr,
> > > + const char *buf, size_t size)
> > > +{
> > > + enum battery_charging_mode mode;
> > > + const char *label;
> > > + int ret = -EINVAL;
> > > +
> > > + for (mode = DELL_BAT_MODE_STANDARD; mode < DELL_BAT_MODE_MAX; mode++) {
> > > + label = battery_state[mode];
> > > + if (label && sysfs_streq(label, buf))
> > > + break;
> > > + }
> > > +
> > > + if (mode > DELL_BAT_MODE_NONE && mode < DELL_BAT_MODE_MAX) {
> > > + ret = battery_charging_mode_set(mode);
> > > + if (!ret) {
> > > + bat_chg_current = mode;
> > > + ret = size;
> > > + }
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static ssize_t charge_control_start_threshold_show(struct device *dev,
> > > + struct device_attribute *attr,
> > > + char *buf)
> > > +{
> > > + int ret, start;
> > > +
> > > + ret = dell_battery_read_req(BAT_CUSTOM_CHARGE_START, &start);
> > > + if (!ret)
> > > + ret = sysfs_emit(buf, "%d\n", start);
> > > +
> > > + return ret;
> > > +}
> >
> > This function and also following 3 functions have unusual error
> > handling. Normally error handling is done by early return, as:
> >
> > ret = func1();
> > if (ret)
> > return ret;
> >
> > ret = func2();
> > if (ret)
> > return ret;
> >
> > return 0;
> >
> > You can change it something like:
> >
> > {
> > int ret, start;
> >
> > ret = dell_battery_read_req(BAT_CUSTOM_CHARGE_START, &start);
> > if (ret)
> > return ret;
> >
> > return sysfs_emit(buf, "%d\n", start);
> > }
> >
>
> Okay.
>
>
> > > +static ssize_t charge_control_start_threshold_store(struct device *dev,
> > > + struct device_attribute *attr,
> > > + const char *buf, size_t size)
> > > +{
> [...]
>
> > > +
> > > +static void __init dell_battery_init(struct device *dev)
> > > +{
> > > + enum battery_charging_mode current_mode = DELL_BAT_MODE_NONE;
> > > +
> > > + dell_battery_read_req(BAT_CUSTOM_MODE_TOKEN, (int *) &current_mode);
> > > + if (current_mode != DELL_BAT_MODE_NONE) {
> >
> > I quite do not understand how is this code suppose to work.
> >
> > Why is there mix of custom kernel enum battery_charging_mode and return
> > value from Dell's API?
>
> This is from the original patch from Dell; tbh, I'm not sure. It does
> work, though. That is, current_mode ends up holding the correct value
> based on what was previously set, even if the charging mode is set from
> the BIOS.
>
> I just scanned through the libsmbios code to see what it's doing, and
> it appears to loop through every charging mode to check if its active.
> I'm not really sure that makes much more sense, so I'll try some more
> tests.

Keyboard backlight code (kbd_get_first_active_token_bit) is doing also
this type scan. If I remember correctly, for every keyboard backlight
token we just know the boolean value - if the token is set or not.

It would really nice to see what (raw) value is returned by the
dell_battery_read_req(token) function for every battery token and for
every initial state.

Because it is really suspicious if dell_battery_read_req() would return
value of the enum battery_charging_mode (as this is kernel enum).

Also another important thing. In past it was possible to buy from Dell
special batteries with long warranty (3+ years). I'm not sure if these
batteries are still available for end-user customers. With this type of
battery, it was not possible to change charging mode to ExpressCharge
(bios option was fade-out). I do not have such battery anymore, but I
would expect that the firmware disabled BAT_EXPRESS_MODE_TOKEN as mark
it as unavailable.

I think that we should scan list of available tokens, like it is done
for keyboard backlight in kbd_init_tokens(). And export via sysfs only
those battery modes for which there is available token.

>
> >
> > My feeling is that dell_battery_read_req(BAT_CUSTOM_MODE_TOKEN) checks
> > if the token BAT_CUSTOM_MODE_TOKEN is set or not.
> >
> > Could you please check what is stored in every BAT_*_MODE_TOKEN token at
> > this init stage?
> >
> > I think it should work similarly, like keyboard backlight tokens as
> > implemented in functions: kbd_set_token_bit, kbd_get_token_bit,
> > kbd_get_first_active_token_bit.
> >
> > > + bat_chg_current = current_mode;
> > > + battery_hook_register(&dell_battery_hook);
> > > + }
> > > +}
> > > +
> [...]
>
> > > #define GLOBAL_MUTE_ENABLE 0x058C
> > > #define GLOBAL_MUTE_DISABLE 0x058D
> > >
> > > +enum battery_charging_mode {
> > > + DELL_BAT_MODE_NONE = 0,
> > > + DELL_BAT_MODE_STANDARD,
> > > + DELL_BAT_MODE_EXPRESS,
> > > + DELL_BAT_MODE_PRIMARILY_AC,
> > > + DELL_BAT_MODE_ADAPTIVE,
> > > + DELL_BAT_MODE_CUSTOM,
> > > + DELL_BAT_MODE_MAX,
> > > +};
> > > +
> >
> > I think that this is just an internal driver enum, not Dell API. So this
> > enum should be in the dell-laptop.c file.
> >
>
> Agreed, I'll change it.
>
>
>
>
> --
> I'm available for contract & employment work, see:
> https://spindle.queued.net/~dilinger/resume-tech.pdf