Am Sonntag, den 26.06.2016, 09:05 -0500 schrieb Rob Herring: > On Sun, Jun 26, 2016 at 12:21 AM, Phil Reid <preid@xxxxxxxxxxxxxxxxx> wrote: > > G'day Rob > > > > Couple of thoughts / question below. > > > > On 25/06/2016 01:50, Rob Herring wrote: > >> > >> On Wed, Jun 22, 2016 at 09:07:15PM +0200, Karl-Heinz Schneider wrote: > >>> > >>> This patch adds device tree documentation for the sbs-manager > >>> > >>> Reviewed-by: Phil Reid <preid@xxxxxxxxxxxxxxxxx> > >>> Signed-off-by: Karl-Heinz Schneider <karl-heinz@xxxxxxxxxxxxxxxxx> > >>> --- > >>> .../devicetree/bindings/power/sbs,sbs-manager.txt | 58 > >>> ++++++++++++++++++++++ > >>> 1 file changed, 58 insertions(+) > >>> create mode 100644 > >>> Documentation/devicetree/bindings/power/sbs,sbs-manager.txt > >>> > >>> diff --git a/Documentation/devicetree/bindings/power/sbs,sbs-manager.txt > >>> b/Documentation/devicetree/bindings/power/sbs,sbs-manager.txt > >>> new file mode 100644 > >>> index 0000000..d52b466 > >>> --- /dev/null > >>> +++ b/Documentation/devicetree/bindings/power/sbs,sbs-manager.txt > >>> @@ -0,0 +1,58 @@ > >>> +Binding for sbs-manager > >>> + > >>> +Required properties: > >>> +- compatible: should be "sbs,sbs-manager" or "lltc,ltc1760" if device is > >>> a > >>> + ltc1760. > >> > >> > >> sbs is not a vendor. What chip is sbs-manager? I suspect you should drop > >> it and only list specific chips. > > > > This follows the interface to the existing paired sbs,sbs-battery driver > > defined in power/sbs-battery.c > > It implements a generic driver for the Smart Battery System Manager > > Specification. > > Spec available here: http://sbs-forum.org/specs/sbsm100b.pdf > > > > In addition the ltc1760 extends the spec. > > Chips will always vary from specs in some way either on purpose or by > accident. sbs,sbs-manager is fine as a fallback string, but there > should always be a chip specific string first. All right. Will change compatible string to "lltc,ltc1760" and mention in the Required properties section that "sbs,sbs-manager" is usable as fallback. > > >>> +- reg: integer, i2c address of the device. Should be <0xa>. > >>> + > >>> +Optional properties: > >>> +- sbsm,i2c-retry-count: integer, number of retries for trying to read or > >>> write > >>> + to registers. Default: 1 > >> > >> > >> Seems like a driver setting. Is having a retry in the driver a problem > >> if the h/w works and never actually needs it? > > > > Similarly the sbs-battery driver specifies the same same retry behaviour. > > And is a model for this implementation. > > > > I've found the ltc1760 and sbs batteries to be problematic when > > communicating to them. > > A lot of drivers (and the associated hardware) don't handle multiple bus > > masters well. > > The bus arbitation doesn't seem to work correctly. > > Retries where the only thing I could do to to get things to work reliably. > > Mostly means the driver needs fixing, but in one case the designware core > > hardware seemed to be the problem for me. > > I'm not questioning the need for a retry. I'm questioning the need to > limit the retries and tune per platform. What would be the issue if > the driver hardcodes the number of retries to 10? This will work for > any h/w that needs 0, 1, 2, ..., or 10 retries. The only issue would > be how long until it errors out. > > And yes, I can confirm DW i2c h/w is a POS at least for some versions. > > >>> +From OS view the device is basically an i2c-mux used to communicate with > >>> up to > >>> +four smart battery devices at address 0xb. The driver actually > >>> implements this > >>> +behaviour. So standard i2c-mux nodes can be used to register up to four > >>> slave > >>> +batteries. Channels will be numerated as 1, 2, 4 and 8. > >>> + > >>> +Example: > >>> + > >>> +batman@0a { > >>> + compatible = "sbs,sbs-manager"; > >>> + reg = <0x0a>; > >>> + sbsm,i2c-retry-count = <3>; > >>> + #address-cells = <1>; > >>> + #size-cells = <0>; > >>> + > >>> + channel1@1 { > >> > >> > >> channel@1 > >> > >> Do we have a standard node name for mux nodes? If not, we should. > >> > >>> + #address-cells = <1>; > >>> + #size-cells = <0>; > >>> + reg = <1>; > >>> + > >>> + battery1@0b { > >> > >> > >> battery@b > >> > >>> + compatible = "sbs-battery"; > >> > >> > >> This should be an actual battery model. Or all this information is > >> generic, you don't really need it in DT. > > > > Do we really want to restrict to battery model? > > You're not. It is just being explicit in case some battery needs > special handling and you only find that out after writing the binding. > The DT model is such that the kernel can be updated with fixes without > updating the DT. Specific compatible strings are needed for that to > work. > > > I have hardware where complete different sbs compliant batteries can be > > plugged in. > > Without the compatible flag here how do you get the sbs-battery driver to > > load and manage the battery itself? > > Or are you suggesting the manager should do this somehow? > > I'm still learning... > > sbs,sbs-battery can still be a fall-back compatible string. Consider this scenario: compatible = "ti,bq2060", "sbs,sbs-battery"; By now the there is no special "bq2060" driver. But my battery might be on of those. I code the DT this way everything should work find (sbs-battery driver will bind). If battery is removable and battery device changes everything should still work fine hence sbs-battery works on subset of registers of the standard. But what happens if a kernel update is done and a bq2060 driver appears which might want access to registers not part of the standard and the (now changed) device doesn't provide? > > Rob Karl-Heinz -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
