On 8/15/19 6:50 PM, Saravana Kannan wrote: > On Wed, Aug 7, 2019 at 7:06 PM Frank Rowand <frowand.list@xxxxxxxxx> wrote: >> >> On 7/23/19 5:10 PM, Saravana Kannan wrote: >>> Add device-links after the devices are created (but before they are >>> probed) by looking at common DT bindings like clocks and >>> interconnects. < very big snip (lots of comments that deserve answers) > >> >> /** >> * of_link_property - TODO: >> * dev: >> * con_np: >> * prop: >> * >> * TODO... >> * >> * Any failed attempt to create a link will NOT result in an immediate return. >> * of_link_property() must create all possible links even when one of more >> * attempts to create a link fail. >> >> Why? isn't one failure enough to prevent probing this device? >> Continuing to scan just results in extra work... which will be >> repeated every time device_link_check_waiting_consumers() is called > > Context: > As I said in the cover letter, avoiding unnecessary probes is just one > of the reasons for this patch. The other (arguably more important) Agree that it is more important. > reason for this patch is to make sure suppliers know that they have > consumers that are yet to be probed. That way, suppliers can leave > their resource on AND in the right state if they were left on by the > bootloader. For example, if a clock was left on and at 200 MHz, the > clock provider needs to keep that clock ON and at 200 MHz till all the > consumers are probed. > > Answer: Let's say a consumer device Z has suppliers A, B and C. If the > linking fails at A and you return immediately, then B and C could > probe and then figure that they have no more consumers (they don't see > a link to Z) and turn off their resources. And Z could fail > catastrophically. Then I think that this approach is fatally flawed in the current implementation. A device can be added by a module that is loaded. In that case the device was not present at late boot when the suppliers may turn off their resources. (I am assuming the details since I have not reviewed the patches later in the series that implement this part.) Am I missing something? If I am wrong, then I'll have more comments for your review replies for patches 2 and 3. > < another snip > > Thanks, > Saravana > -Frank
