On Mon, Jun 20, 2016 at 11:38 AM, Jan Beulich <jbeul...@suse.com> wrote:
> >>> On 20.06.16 at 17:15, <andrey2...@gmail.com> wrote: > > On Mon, Jun 20, 2016 at 4:56 AM, Jan Beulich <jbeul...@suse.com> wrote: > > > >> >>> On 20.06.16 at 00:03, <andrey2...@gmail.com> wrote: > >> > Follow up on > >> http://www.gossamer-threads.com/lists/xen/devel/436000#436000 > >> > Using > >> http://eli.thegreenplace.net/2008/08/15/intersection-of-1d-segments as > >> > reference. > >> > > >> > New value > >> > |---------------| > >> > > >> > f1 f5 > >> > |---| |-----| > >> > f2 f4 > >> > |-----| f3 |-----| > >> > |-----| > >> > > >> > Given a new value of the type above, Current logic will not > >> > allow applying parts of the new value overlapping with f3 filter. > >> > only f2 and f4. > >> > >> I remains unclear what f1...f5 are meant to represent here. > >> > > > > f1-f5 would be config_field[] such as header_common in > conf_space_header.c > > or any other config_field added (by adding quirks for example). > > > >> > >> > This change allows all 3 types of overlapes to be included. > >> > More specifically for passthrough an Industrial Ethernet Interface > >> > (Hilscher GmbH CIFX 50E-DP(M/S)) on a HVM DomU running the > >> > Xen 4.6 Hypervisor it allows to restore the LATENCY TIMER field > >> > given a quirk to allow read/write for that field is already in place. > >> > Device driver logic is such that the entire confspace is > >> > written in 4 byte chunks s.t. LATENCY_TIMER AND CACHE_LINE_SIZE are > >> > arriving together in one call to xen_pcibk_config_write. > >> > >> Tweaks to make individual devices work are dubious. Any > >> explanation should outline why current behavior is _generally_ > >> wrong. In particular with the original issue being with the > >> Latency Timer field, and with that field now being allowed to > >> be written by its entry in header_common[], ... > > > > > > To me current behaviour looks generally inconsistent because given a > > request to wrote > > 4 bytes starting with 0xC let's look what's happening > > inside xen_pcibk_config_write > > > > *[81664.632262 < 0.000035>] xen-pciback: 0000:06:00.0: write request 4 > > bytes at 0xc = 4000* > > *[81664.632264 < 0.000002>] xen-pciback: 0000:06:00.0: read 1 bytes at > > 0xc* > > *[81664.632275 < 0.000011>] xen-pciback: 0000:06:00.0: read 1 bytes at > > 0xc = 0 * > > *[81664.632282 < 0.000002>] xen-pciback: 0000:06:00.0: read 1 bytes at > > 0xf* > > *[81664.632292 < 0.000010>] xen-pciback: 0000:06:00.0: read 1 bytes at > > 0xf = 0* > > > > So you can see that current logic will allow to read/write 0xc which > > is PCI_CACHE_LINE_SIZE, > > skips PCI_LATENCY_TIMER also there is a quirk in place there which allows > > writes to this memory, > > skips 0xE (which is fine since this field is not allowed to be accessed) > > and then writes 0xf PCI_BIST > > > > So using my previous sketch adjusted for this use case > > > > |----4b write request starting at 0xc----| > > > > |--f1--| |--f2--| |--f3--| > > > > Where > > f1 == PCI_CACHE_LINE_SIZE > > f2 == PCI_LATENCY_TIMER > > f3 == PCI_BIST > > > > With ciurrent logic Only f1 and f3 are allowed but not f2 even when there > > is a field and > > a quirk in place allowing read write access to that memory location. > > Let's leave quirks out of the picture for now. And without quirk, > f2 is not writable (and cannot be made by adding a quirk, as > explained before). > > Yes, i guess due to not allowing duplicates. > > To me it seems as a generally inconsistent behaviour and not specifically > > related to our driver. > > > > With my patch (and a fix from || to && Thanks a lot for pointing this out > > to me.) > > f1, f2 and f3 are being treated the same which IMHO is more correct. > > Hmm, with that and the >= -> > adjustment, I can't really see > how your variant is different from the original (other than being > more compact). What am I overlooking here? > > >> > --- a/drivers/xen/xen-pciback/conf_space.c > >> > +++ b/drivers/xen/xen-pciback/conf_space.c > >> > @@ -230,8 +230,7 @@ int xen_pcibk_config_write(struct pci_dev *dev, > int > >> > offset, int size, u32 value) > >> > field_start = OFFSET(cfg_entry); > >> > field_end = OFFSET(cfg_entry) + field->size; > >> > > >> > - if ((req_start >= field_start && req_start < field_end) > >> > - || (req_end > field_start && req_end <= field_end)) > { > >> > + if (req_end >= field_start || field_end >= req_start) { > >> > tmp_val = 0; > >> > >> ... any change to the logic here which results in writes to the field > >> getting issued would seem wrong without even looking at the > >> particular nature of the field. > > > > I am not sure I understand - please clarify. > > See above - to me the original expression looks (a) correct and > (b) identical in effect to the corrected version of yours. Hence > if behavior changes, something must be wrong in either old or new > code, and due to (a) I would imply it's in the new one. But as said > above - I guess I'm missing something here. > Here is printouts with applying the new logic [ 382.222213] xen-pciback: 0000:06:00.0: write request 4 bytes at 0xc = 4000 [ 382.222214] xen-pciback: 0000:06:00.0: read 1 bytes at 0xc [ 382.222228] xen-pciback: 0000:06:00.0: read 1 bytes at 0xc = 0 [ 382.222238] xen-pciback: 0000:06:00.0: read 1 bytes at 0xd [ 382.222281] xen-pciback: 0000:06:00.0: read 1 bytes at 0xd = 0 [ 382.222313] xen-pciback: 0000:06:00.0: read 1 bytes at 0xf [ 382.222341] xen-pciback: 0000:06:00.0: read 1 bytes at 0xf = 0 So from prints the logic is not equivalent. 0xd is included in this case. In original logic field 0xd is excluded because Not if ((req_start >= field_start && req_start < field_end) Nor (req_end > field_start && req_end <= field_end)) evaluate to true. Where request would be 4b segment starting with 0xc While f (req_end >= field_start && field_end >= req_start) will evaluate for true in this case. Unless I am missing something... > > Jan > Andrey
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