On Wed, Mar 06, 2019 at 02:35:53PM -0700, Logan Gunthorpe wrote:
On 2019-03-06 1:26 p.m., Serge Semin wrote:
First of all, It might be unsafe to have some resources consumed by NTB MSI or some other library without a simple way to warn NTB client drivers about their attempts to access that resources, since it might lead to random errors. When I thought about implementing a transport library based on the Message/Spad+Doorbell registers, I had in mind to create an internal bits-field array with the resources busy-flags. If, for instance, some message or scratchpad register is occupied by the library (MSI, transport or some else), then it would be impossible to access these resources directly through NTB API methods. So NTB client driver shall retrieve an error in an attempt to write/read data to/from busy message or scratchpad register, or in an attempt to set some occupied doorbell bit. The same thing can be done for memory windows.
Yes, it would be nice to have a generic library to manage all the resources, but right now we don't and it's unfair to expect us to take on this work to get the features we care about merged. Right now, it's not at all unsafe as the client is quite capable of ensuring it has the resources for the MSI library. The changes for ntb_transport to ensure this are quite reasonable.
Second tiny concern is about documentation. Since there is a special file for all NTB-related doc, it would be good to have some description about the NTB MSI library there as well: Documentation/ntb.txt
Sure, I'll add a short blurb for v3. Though, I noticed it's quite out of date since your changes. Especially in the ntb_tool section...
Ok. Thanks. If you want you can add some info to the ntb_tool section as well. If you don't have time, I'll update it next time I submit anything new to the subsystem.
-Sergey
- u32 *peer_mws[];
Shouldn't we use the __iomem attribute here since later the devm_ioremap() is used to map MWs at these pointers?
Yes, will change for v3.
Simpler and faster cleanup-code would be:
- unroll:
- for (--i; i >= 0; --i)
devm_iounmap(&ntb->dev, ntb->msi->peer_mws[i]);Faster, maybe, but I would not consider this simpler. It's much more complicated to reason about and ensure it's correct. I prefer my way because I don't care about speed, but I do care about readability.
Alas calling the ntb_mw_set_trans() method isn't enough to fully initialize NTB Memory Windows. Yes, the library will work for Intel/AMD/Switchtec (two-ports legacy configuration), but will fail for IDT due to being based on the outbound MW xlat interface. So the library at this stage isn't portable across all NTB hardware. In order to make it working the translation address is supposed to be transferred to the peer side, where a peer code should call ntb_peer_mw_set_trans() method with the retrieved xlat address. See documentation for details:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Docume...
ntb_perf driver can be also used as a reference of the portable NTB MWs setup.
Gross. Well, given that ntb_transport doesn't even support this and we don't really have a sensible library to transfer this information, I'm going to leave it as is for now. Someone can update ntb_msi when they update ntb_transport, preferably after we have a nice library to handle the transfers for us seeing I absolutely do not want to replicate the mess in ntb_perf.
Actually, if we had a generic spad/msg communication library, it would probably be better to have a common ntb_mw_set_trans() function that uses the communications library to send the data and automatically call ntb_peer_mw_set_trans() on the peer. That way we don't have to push this mess into the clients.
The same cleanup pattern can be utilized here: +error_out:
- for (--peer; peer >= 0; --peer) {
peer_widx = ntb_peer_highest_mw_idx(ntb, peer);ntb_mw_clear_trans(ntb, i, peer_widx);- }
So you won't need "i" variable here anymore. You also don't need to check the return value of ntb_peer_highest_mw_idx() in the cleanup loop because it was already checked in the main algo code.
See above.
+EXPORT_SYMBOL(ntb_msi_clear_mws);
Similarly something like ntb_msi_peer_clear_mws() should be added to unset a translation address on the peer side.
Well, we can table that for when ntb_msi supports the peer MW setting functions.
+int ntb_msi_peer_trigger(struct ntb_dev *ntb, int peer,
struct ntb_msi_desc *desc)+{
- int idx;
- if (!ntb->msi)
return -EINVAL;- idx = desc->addr_offset / sizeof(*ntb->msi->peer_mws[peer]);
- ntb->msi->peer_mws[peer][idx] = desc->data;
Shouldn't we use iowrite32() here instead of direct access to the IO-memory?
Yes, as above I'll fix it for v3.
@@ -425,6 +427,10 @@ struct ntb_dev { spinlock_t ctx_lock; /* block unregister until device is fully released */ struct completion released;
- #ifdef CONFIG_NTB_MSI
- struct ntb_msi *msi;
- #endif
I'd align the macro-condition to the most left position: +#ifdef CONFIG_NTB_MSI
- struct ntb_msi *msi;
+#endif
Fixed for v3.
Logan
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