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Tue, 26 Feb 2019 21:04:59 -0800 (PST) Subject: Re: [PATCH 2/2] drivers/misc: Add Aspeed P2A control driver To: Patrick Venture , arnd@arndb.de, gregkh@linuxfoundation.org, joel@jms.id.au, andrew@aj.id.au References: <20190221222537.137331-1-venture@google.com> From: Florian Fainelli Openpgp: preference=signencrypt Autocrypt: addr=f.fainelli@gmail.com; keydata= mQENBFPAG8ABCAC3EO02urEwipgbUNJ1r6oI2Vr/+uE389lSEShN2PmL3MVnzhViSAtrYxeT M0Txqn1tOWoIc4QUl6Ggqf5KP6FoRkCrgMMTnUAINsINYXK+3OLe7HjP10h2jDRX4Ajs4Ghs JrZOBru6rH0YrgAhr6O5gG7NE1jhly+EsOa2MpwOiXO4DE/YKZGuVe6Bh87WqmILs9KvnNrQ PcycQnYKTVpqE95d4M824M5cuRB6D1GrYovCsjA9uxo22kPdOoQRAu5gBBn3AdtALFyQj9DQ KQuc39/i/Kt6XLZ/RsBc6qLs+p+JnEuPJngTSfWvzGjpx0nkwCMi4yBb+xk7Hki4kEslABEB AAG0KEZsb3JpYW4gRmFpbmVsbGkgPGZhaW5lbGxpQGJyb2FkY29tLmNvbT6JAccEEAECALEF AlPAG9YXCgABv0jL/n0t8VEFmtDa8j7qERo7AN0gFAAAAAAAFgABa2V5LXVzYWdlLW1hc2tA cGdwLmNvbY4wFIAAAAAAIAAHcHJlZmVycmVkLWVtYWlsLWVuY29kaW5nQHBncC5jb21wZ3Bt aW1lCAsJCAcDAgEKAhkBBReAAAAAGRhsZGFwOi8va2V5cy5icm9hZGNvbS5jb20FGwMAAAAD FgIBBR4BAAAABBUICQoACgkQgTG1xCm8ZqD+Dgf9HhhzqvJYIPomNeg+ll7/TbzWb871E+HQ TaufJQFQwLEbgdFSZO2uj4UqfDpCyTwtHTVMJogWt3pCAE1sadeIY8OlT6918ofKIl8AiHj2 BlfL7ASZ5wzkRMt/4TZoinq9O1tPEynb5G6PdZTV3UQtmSGnpt2EOu7KtRJsnThBiXoOO9TJ Asg4vXJ0ZM1y/MPhQlZbPCHQZFe1gaVWBPLGnLyWyeprqgSLWHaGqrUhlfK1sLuJK1bjYDCI NetK0pS4cA4ZJgogr5FrtV64R19zLl02mt/Yj7rAmjC3ZBuwVi3V35kD8Kd4d9QM2apsiILV bzGbtVCSUgvxI+1SsJEm3bkBDQRTwBvBAQgArGvvWip77T4xgJztZp9YRylAcVTC9gtx0Gg6 eYk/EPANGm9TkuGpI++T/Il2H2TjFQNC7eubWohbYj0+6Tmf8nP+VmyobDxPXcMrK7x4xy9o D+Kub2Vf0SXbsM8fL/SqzGbFWZSm73L1L4GZoxvYIz0i7LExYSX2u5YVLaMBaH9HwKt2cvr7 MuTrRHtcbOZImoXT29g2UnoF1uwxYNeRhZY/lRvVkkY0lDipPuDwg3SpfHMtCybPq1uAswQd gEbHzRsEXwCR1OF3pIuGt4I3tSEhH/k1caqi0BlqjbGUOkku44xC2gf1ZU267FBBkdV3yJ/7 KnrJEnkMCYhS3kII9wARAQABiQJBBBgBAgErBQJTwBvCBRsMAAAAwF0gBBkBCAAGBQJTwBvB AAoJEJNgBqiYLw9VDRUIAJaTef6hsUAESnlGDpC+ymL2RZdzAJx9lXjU4hhaFcyhznuyyMJq d3mehmLxsqDRvHDiqyD71w2Bnc838MVZw0pwBPdnb/h9Ocmp0lL/9hwSGWvy4az5lYVyoA9u 14UIzh0YNGu6jr0isd/LJAbHXqwJwWWs3y8PTrpEp68V6lv+aXt5gR03lJEAvIR1Awp4JJ/e Z5y12gQISp0X8xal9YhhDWER92YLYrO2b6Hc2S31lAupzfCw8lmZsP1PRz1GmF/KmDD9J9N/ b8IehhWQqrBQjMjn2K2XkvN75HnAMHKFYfHZR3ZHtK52ZP1crV7THtbtrnPXVDq+vO4QPmdC +SEACgkQgTG1xCm8ZqC6BwgAl3kRh7oozpjpG8jpO8en5CBtTl3G+OpKJK9qbQyzdCsuJ0K1 qe1wZPZbP/Y+VtmqSgnExBzjStt9drjFBK8liPQZalp2sMlS9S7csSy6cMLF1auZubAZEqpm tpXagbtgR12YOo57Reb83F5KhtwwiWdoTpXRTx/nM0cHtjjrImONhP8OzVMmjem/B68NY++/ qt0F5XTsP2zjd+tRLrFh3W4XEcLt1lhYmNmbJR/l6+vVbWAKDAtcbQ8SL2feqbPWV6VDyVKh ya/EEq0xtf84qEB+4/+IjCdOzDD3kDZJo+JBkDnU3LBXw4WCw3QhOXY+VnhOn2EcREN7qdAK w0j9Sw== Message-ID: <9ab3a0e6-fa1e-11c7-adad-7e14bfe28059@gmail.com> Date: Tue, 26 Feb 2019 21:04:52 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190221222537.137331-1-venture@google.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190226_210502_584553_6388AE74 X-CRM114-Status: GOOD ( 18.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-aspeed@lists.ozlabs.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2/21/2019 2:25 PM, Patrick Venture wrote: > The ASPEED AST2400, and AST2500 in some configurations include a > PCI-to-AHB MMIO bridge. This bridge allows a server to read and write > in the BMC's memory space. This feature is especially useful when using > this bridge to send large files to the BMC. > > The host may use this to send down a firmware image by staging data at a > specific memory address, and in a coordinated effort with the BMC's > software stack and kernel, transmit the bytes. > > This driver enables the BMC to unlock the PCI bridge on demand, and > configure it via ioctl to allow the host to write bytes to an agreed > upon location. In the primary use-case, the region to use is known > apriori on the BMC, and the host requests this information. Once this > request is received, the BMC's software stack will enable the bridge and > the region and then using some software flow control (possibly via IPMI > packets), copy the bytes down. Once the process is complete, the BMC > will disable the bridge and unset any region involved. > > The default behavior of this bridge when present is: enabled and all > regions marked read-write. This driver will fix the regions to be > read-only and then disable the bridge entirely. A complete drive by review, so I could be completely off here (most likely am), but have you considered using virtio and doing some sort of rudimentary features (regions here) negotiation over that interface? If I get your description right in premise maybe emulating the AHB side on the BMC as a PCI end-point device driver, and using it as a seemingly regular PCI EP from the host side with BARs and stuff might make sense here and be less of a security hole than it currently looks like. -- Florian _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel