| Message ID | 20221202223327.690880-2-luzmaximilian@gmail.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | platform/surface: aggregator: Improve target/source handling in SSH messages | expand |
Hi, On 12/2/22 23:33, Maximilian Luz wrote: > It is possible that we (the host/kernel driver) receive command messages > that are not intended for us. Ignore those for now. > > The whole story is a bit more complicated: It is possible to enable > debug output on SAM, which is sent via SSH command messages. By default > this output is sent to a debug connector, with its own target ID > (TID=0x03). It is possible to override the target of the debug output > and set it to the host/kernel driver. This, however, does not change the > original target ID of the message. Meaning, we receive messages with > TID=0x03 (debug) but expect to only receive messages with TID=0x00 > (host). > > The problem is that the different target ID also comes with a different > scope of request IDs. In particular, these do not follow the standard > event rules (i.e. do not fall into a set of small reserved values). > Therefore, current message handling interprets them as responses to > pending requests and tries to match them up via the request ID. However, > these debug output messages are not in fact responses, and therefore > this will at best fail to find the request and at worst pass on the > wrong data as response for a request. > > Therefore ignore any command messages not intended for us (host) for > now. We can implement support for the debug messages once we have a > better understanding of them. > > Note that this may also provide a bit more stability and avoid some > driver confusion in case any other targets want to talk to us in the > future, since we don't yet know what to do with those as well. A warning > for the dropped messages should suffice for now and also give us a > chance of discovering new targets if they come along without any > potential for bugs/instabilities. > > Fixes: c167b9c7e3d6 ("platform/surface: Add Surface Aggregator subsystem") > Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com> Thank you for your patch, I've applied this patch to my fixes branch: https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=fixes Note it will show up in my fixes branch once I've pushed my local branch there, which might take a while. I will include this patch in my next fixes pull-req to Linus for the current kernel development cycle. Regards, Hans > --- > Note: I've simplified this commit so that it can be applied > independently of the rest of the series for easier backporting. > --- > .../surface/aggregator/ssh_request_layer.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/platform/surface/aggregator/ssh_request_layer.c b/drivers/platform/surface/aggregator/ssh_request_layer.c > index f5565570f16c..69132976d297 100644 > --- a/drivers/platform/surface/aggregator/ssh_request_layer.c > +++ b/drivers/platform/surface/aggregator/ssh_request_layer.c > @@ -916,6 +916,20 @@ static void ssh_rtl_rx_command(struct ssh_ptl *p, const struct ssam_span *data) > if (sshp_parse_command(dev, data, &command, &command_data)) > return; > > + /* > + * Check if the message was intended for us. If not, drop it. > + * > + * Note: We will need to change this to handle debug messages. On newer > + * generation devices, these seem to be sent to tid_out=0x03. We as > + * host can still receive them as they can be forwarded via an override > + * option on SAM, but doing so does not change tid_out=0x00. > + */ > + if (command->tid_out != 0x00) { > + rtl_warn(rtl, "rtl: dropping message not intended for us (tid = %#04x)\n", > + command->tid_out); > + return; > + } > + > if (ssh_rqid_is_event(get_unaligned_le16(&command->rqid))) > ssh_rtl_rx_event(rtl, command, &command_data); > else
diff --git a/drivers/platform/surface/aggregator/ssh_request_layer.c b/drivers/platform/surface/aggregator/ssh_request_layer.c index f5565570f16c..69132976d297 100644 --- a/drivers/platform/surface/aggregator/ssh_request_layer.c +++ b/drivers/platform/surface/aggregator/ssh_request_layer.c @@ -916,6 +916,20 @@ static void ssh_rtl_rx_command(struct ssh_ptl *p, const struct ssam_span *data) if (sshp_parse_command(dev, data, &command, &command_data)) return; + /* + * Check if the message was intended for us. If not, drop it. + * + * Note: We will need to change this to handle debug messages. On newer + * generation devices, these seem to be sent to tid_out=0x03. We as + * host can still receive them as they can be forwarded via an override + * option on SAM, but doing so does not change tid_out=0x00. + */ + if (command->tid_out != 0x00) { + rtl_warn(rtl, "rtl: dropping message not intended for us (tid = %#04x)\n", + command->tid_out); + return; + } + if (ssh_rqid_is_event(get_unaligned_le16(&command->rqid))) ssh_rtl_rx_event(rtl, command, &command_data); else
It is possible that we (the host/kernel driver) receive command messages that are not intended for us. Ignore those for now. The whole story is a bit more complicated: It is possible to enable debug output on SAM, which is sent via SSH command messages. By default this output is sent to a debug connector, with its own target ID (TID=0x03). It is possible to override the target of the debug output and set it to the host/kernel driver. This, however, does not change the original target ID of the message. Meaning, we receive messages with TID=0x03 (debug) but expect to only receive messages with TID=0x00 (host). The problem is that the different target ID also comes with a different scope of request IDs. In particular, these do not follow the standard event rules (i.e. do not fall into a set of small reserved values). Therefore, current message handling interprets them as responses to pending requests and tries to match them up via the request ID. However, these debug output messages are not in fact responses, and therefore this will at best fail to find the request and at worst pass on the wrong data as response for a request. Therefore ignore any command messages not intended for us (host) for now. We can implement support for the debug messages once we have a better understanding of them. Note that this may also provide a bit more stability and avoid some driver confusion in case any other targets want to talk to us in the future, since we don't yet know what to do with those as well. A warning for the dropped messages should suffice for now and also give us a chance of discovering new targets if they come along without any potential for bugs/instabilities. Fixes: c167b9c7e3d6 ("platform/surface: Add Surface Aggregator subsystem") Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com> --- Note: I've simplified this commit so that it can be applied independently of the rest of the series for easier backporting. --- .../surface/aggregator/ssh_request_layer.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)