Hi Jeremy, > From: Jeremy Kerr <jk@xxxxxxxxxxxxxxxxxxxx> > Sent: Thursday, September 9, 2021 9:53 AM > > > Yes, there is security concern using HW mode. > > Our designer is considering to remove the HW mode support in the next > > generation of Aspeed SoCs. > > So far we haven't encountered a scenario demanding HW mode. > > Great to hear :) can we unconditionally set ESPI000[9] in the driver then? Yes for the v5 revision. As HW mode is going to be eliminated in the future. A brief explanation will also be added. > > > > With than in mind, if we're disabling hardware mode - what does the > > > direction control setting effect when we're in software mode > > > (ESPICTRL[9] == 1)? Does it even matter? > > > > Yes, the direction matters even in SW mode. > > When the direction is 'master-to-slave' and the GPIO value is updated > > by the Host through PUT_VW, a VW interrupt is trigger to notify BMC. > > For the 'slave-to-master' GPIO, a alert is generated to notify the > > Host to issue GET_VW for the GPIO value updated by the BMC by ESPI09C. > > OK, but the datasheet mentions that ESPICFG804 is only applicable when > ESPI000[9] = 0, or is that not the case? Yes, ESPICFG804 is applicable only on HW mode (ESPI000[9]=0). When the HW mode is selected, the eSPI slave forwards GPIO update in PUT_VW packet sent by the Host to the physical GPIO based on the ESPICFG804 mapping. This is purely done by HW. No interrupts will be generated to notify SW. > > But based on what you've said: yes, it sounds like the generic gpiodev parts > won't be useful for this. > > > > Separate from this: I'm also proposing that we represent the system > > > event VWs as gpiodevs as well. > > > > > > > A raw packet, primitive interface should have better flexibility > > > > to manage MCTP packets over the OOB channel. > > > > > > OK, let me phrase this differently: can the OOB channel be used for > > > anything other than SMBus messaging? Is it useful to provide an > > > interface that isn't a standard SMBus/i2c device? > > > > Yes, the PCH spec. also defines two additional packet format for an > > eSPI slave to retrieve PCH Temperature Data and RTC time. > > It should be trivial to prepare a byte buffer in that format and send > > it through the raw packet interface. > > OK, understood. > > > > If you need custom uapi definitions for this driver, that might be > > > okay, but it's going to be more work for you (to define an interface > > > that can be supported long-term), rather than using standard > > > infrastructure that already exists. > > > > Thus I suggested that we can refer to the IPMI KCS BMC driver, which > > supports the selection of different user interfaces, RAW or IPMI. > > Yep, but the KCS "raw" register set is standardised as part of the IPMI spec too, > which helps to define a stable user API. We don't have that in this case. > > Overall though, if you want to start with the "low-level" API, then introduce > "enhanced" functionality - like an actual SMBus driver - alongside that, then > that sounds like an OK approach. > > > If IOCTL is considered to be not user friendly or magic code > > polluting, file-based read/write on the miscdevice node is also an > > option. > > It's not really my decision to make, but a read/write event interface would > seem to be more consistent to me. Is there an obvious event format that would > be common across all channels, perhaps? We'd probably also need a poll too - > to make use of incoming events, like master-to-slave VW changes, perhaps? A file-based read/write/poll interface is OK to me as well. The main concern is about the peripheral and the VW channels. For the peripheral channel, it takes two miscdevice to export TX/RX interfaces for posted and non-posted packets, respectively. And for the VW channel, the settings GPIO direction is RO and that of GPIO value is RW. And these two should be exported individually.