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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Dec 2020 08:33:53.2600 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 61950053-d3dd-4b1e-66cc-08d89a8ad46f X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: AM5EUR03FT006.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB6PR0801MB1749 Hello Stefano, > On 3 Dec 2020, at 6:47 pm, Stefano Stabellini wr= ote: >=20 > On Thu, 3 Dec 2020, Rahul Singh wrote: >>> On 3 Dec 2020, at 4:13 am, Stefano Stabellini = 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 >>>>>=20 >>>>> Given all the changes to the file by the previous patches we are >>>>> basically fully (or almost fully) adapting this code to Xen. >>>>>=20 >>>>> So at that point I wonder if we should just as well make these change= s >>>>> (e.g. s/of_phandle_args/dt_phandle_args/g) to the code too. >>>>=20 >>>> I have already accepted the fact that keeping Linux code as-is is near= ly >>>> impossible without much workaround :). The benefits tends to also limi= ted as >>>> we noticed for the SMMU driver. >>>>=20 >>>> I would like to point out that this may make quite difficult (if not >>>> impossible) to revert the previous patches which remove support for so= me >>>> features (e.g. atomic, MSI, ATS). >>>>=20 >>>> 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 usef= ul in >>>> the near future (at least MSI, ATS). >>>=20 >>> (I am fine with keeping the Linux code style.) >>>=20 >>> We could try to keep the code as similar to Linux as possible. This >>> didn't work out in the past. >>>=20 >>> Otherwise, we could fully adapt the driver to Xen. If we fully adapt th= e >>> 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. >>>=20 >>>=20 >>> 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. >>>=20 >>> 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. >>>=20 >>> It looks like MSI could be disabled adding a couple of lines to >>> arm_smmu_setup_msis. >>>=20 >>> Similarly ATS seems to be easy to disable by forcing ats_enabled to >>> false. >>>=20 >>> So yes, this looks like a good way forward. Rahul, what do you think? >>=20 >>=20 >> I am ok to have the PCI ATS and MSI functionality in the code.=20 >> As per the discussion next version of the patch will include below modif= ication:Please let me know if there are any suggestion overall that should = be added in next version. >>=20 >> 1. Keep the PCI ATS and MSI functionality code. >=20 > 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 Yes I will disable the feature. >=20 >=20 >> 2. Make the code with XEN compatible ( remove linux compatibility functi= ons) >> 3. Keep the Linux coding style for code imported from Linux. >> 4. Fix all comments. >=20 > Sounds good. >=20 >=20 >> I have one query what will be coding style for new code to make driver w= ork for XEN ?=20 >=20 > 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). Ok. Regards, Rahul =