Hey Ricardo,
On 20-04-16 10:01, Ricardo Ribalda Delgado wrote:
Hi Ollivier
On Wed, Apr 20, 2016 at 9:21 AM, Olliver Schinagl <oliver@xxxxxxxxxxx> wrote:
What I am propossing is at probe():
replace:
if (pdata) {
/* Configure output: open-drain or totem pole (push-pull) */
if (pdata->outdrv == PCA963X_OPEN_DRAIN)
i2c_smbus_write_byte_data(client, PCA963X_MODE2, 0x01);
else
i2c_smbus_write_byte_data(client, PCA963X_MODE2, 0x05);
}
with something like (forgive the spacing):
u8 mode2 = PCA963X_MODE2_DMBLNK | 0x1;
if (pdata && pdata->outdrv == PCA963X_OPEN_DRAIN)
mode2 |= 0x4;
i2c_smbus_write_byte_data(pca963x->chip->client, PCA963X_MODE2, mode2);
and then remove from pca963x_blink() these lines:
u8 mode2 = i2c_smbus_read_byte_data(pca963x->chip->client,
PCA963X_MODE2);
if (!(mode2 & PCA963X_MODE2_DMBLNK))
i2c_smbus_write_byte_data(pca963x->chip->client, PCA963X_MODE2,
mode2 | PCA963X_MODE2_DMBLNK);
As I said before, the reason for this proposal is that the code NEVER
clears PCA963X_MODE2_DMBLNK, only sets it.
Unfortunately I do not have the HW to test this change.
The code never clears it, but the hardware does. So we have to set it
everytime we enable blink.
So I don't think this can work at all, as you now never enable blink
(when you enable it from user space, at probe it works fine via the
default trigger).
What about storing the mode2 register on the chip level, since we never
change it after probe, and only toggle the blink bit in blink_set() and
write the stored mode2 register
so i2c_write(pca963x->chip->mode2 | MODE2_DMBLNK)
The only advantage I see here though is that we save a read + (quite
likley) potentially a write, with an always write. So it saves 1 i2c
read command.
Olliver
Now I understand your concern, the i2c operations are slow and time
consuming making the mutex very expensive.
The thing is, to be able to write the blink bit, we need to read the whole
mode2 register, to do a proper read-modify-write. We don't know what's in
the mode2 register and we only want to write the bit if it is actually not
set to begin with, to save a i2c write operation.
As I said earlier, nowhere in the code clears that bit. The bit is
only set. so no reason to read/modify/write. We can set that bit at
probe time and assume that it will not be changed.
We start this function already however with with two write calls of
sequential registers, the grp and pwm enable registers. There is even a call
to automatically update these registers, which I think we'd use
i2c_master_send() to set the address via the auto-increment register and
enable auto increment of these two registers. Now we reduced the 2 seperate
calls into one bigger 'faster' call. So 1 win there. But! it will require us
however to change the other calls to disable auto increment via de mode1
register. Since this is an extra i2c_write operation, it makes the other i2c
writes more expensive, which may happen much more often (enable blink only
happens occasionally, changing the brightness may change a lot (fade in fade
out).
Be careful with that. Sometimes this chips are connected to the smbus,
wich has a limited number of operations/lengths. We should keep the
i2c_smbus_write_byte_data() call, because that makes the driver
compatible with more hardware.
So unless i'm totally misunderstanding something, I don't think we can safe
much here at all.
To be clear: My proposal is that (after being tested), move the set of
DMBLINK to probe, remove the read/modify/write from blink() and keep
the locking as it is now, only protecting ledout.
Also you need to fix the patch that breaks bisect, but I believe that
you are already working on that.
I have reviewed a bit Documentation/device-tree and it seems that
there is already a binding for active-low. Instead of nxp,active-low
you should call it just active-low. But I am not a device-tree expert.
Finally, you mention that you are fixing some checkpatch errors, but I
cannot replicate those in my side :S
ricardo@pilix:~/curro/linux$ scripts/checkpatch.pl -f
drivers/leds/leds-pca963x.c
total: 0 errors, 0 warnings, 439 lines checked
drivers/leds/leds-pca963x.c has no obvious style problems and is ready
for submission.
So maybe the errors you are fixing are introduced by your patches.
About the other style patches, I do not know what is the policy of the
Maintainer in that matter, especially when the driver did not break
originally checkpatch.
Regards!
---
Ricardo
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