On Thu, 3 Dec 2020, Rahul Singh wrote: > > On 3 Dec 2020, at 4:13 am, Stefano Stabellini <sstabell...@kernel.org> > > wrote: > > On Wed, 2 Dec 2020, Julien Grall wrote: > >> On 02/12/2020 02:51, Stefano Stabellini wrote: > >>> On Thu, 26 Nov 2020, Rahul Singh wrote: > >>>> +/* Alias to Xen device tree helpers */ > >>>> +#define device_node dt_device_node > >>>> +#define of_phandle_args dt_phandle_args > >>>> +#define of_device_id dt_device_match > >>>> +#define of_match_node dt_match_node > >>>> +#define of_property_read_u32(np, pname, out) (!dt_property_read_u32(np, > >>>> pname, out)) > >>>> +#define of_property_read_bool dt_property_read_bool > >>>> +#define of_parse_phandle_with_args dt_parse_phandle_with_args > >>> > >>> Given all the changes to the file by the previous patches we are > >>> basically fully (or almost fully) adapting this code to Xen. > >>> > >>> So at that point I wonder if we should just as well make these changes > >>> (e.g. s/of_phandle_args/dt_phandle_args/g) to the code too. > >> > >> I have already accepted the fact that keeping Linux code as-is is nearly > >> impossible without much workaround :). The benefits tends to also limited > >> as > >> we noticed for the SMMU driver. > >> > >> I would like to point out that this may make quite difficult (if not > >> impossible) to revert the previous patches which remove support for some > >> features (e.g. atomic, MSI, ATS). > >> > >> If we are going to adapt the code to Xen (I'd like to keep Linux code style > >> though), then I think we should consider to keep code that may be useful in > >> the near future (at least MSI, ATS). > > > > (I am fine with keeping the Linux code style.) > > > > We could try to keep the code as similar to Linux as possible. This > > didn't work out in the past. > > > > Otherwise, we could fully adapt the driver to Xen. If we fully adapt the > > driver to Xen (code style aside) it is better to be consistent and also > > do substitutions like s/of_phandle_args/dt_phandle_args/g. Then the > > policy becomes clear: the code comes from Linux but it is 100% adapted > > to Xen. > > > > > > Now the question about what to do about the MSI and ATS code is a good > > one. We know that we are going to want that code at some point in the > > next 2 years. Like you wrote, if we fully adapt the code to Xen and > > remove MSI and ATS code, then it is going to be harder to add it back. > > > > So maybe keeping the MSI and ATS code for now, even if it cannot work, > > would be better. I think this strategy works well if the MSI and ATS > > code can be disabled easily, i.e. with a couple of lines of code in the > > init function rather than #ifdef everywhere. It doesn't work well if we > > have to add #ifdef everywhere. > > > > It looks like MSI could be disabled adding a couple of lines to > > arm_smmu_setup_msis. > > > > Similarly ATS seems to be easy to disable by forcing ats_enabled to > > false. > > > > So yes, this looks like a good way forward. Rahul, what do you think? > > > I am ok to have the PCI ATS and MSI functionality in the code. > As per the discussion next version of the patch will include below > modification:Please let me know if there are any suggestion overall that > should be added in next version. > > 1. Keep the PCI ATS and MSI functionality code.
I'll repeat one point I wrote above that I think it is important: please try to disable ATS and MSI without invasive changes, ideally just a couple of lines to force-disable each feature. > 2. Make the code with XEN compatible ( remove linux compatibility functions) > 3. Keep the Linux coding style for code imported from Linux. > 4. Fix all comments. Sounds good. > I have one query what will be coding style for new code to make driver work > for XEN ? We try to keep the same code style for the entirety of a source file. In this case, the whole driver should use Linux code style (both imported code and new code).
