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[94.114.101.228]) by smtp.gmail.com with ESMTPSA id f14sm11119906wrv.17.2019.11.15.05.50.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Nov 2019 05:50:15 -0800 (PST) From: patrick.rudolph@9elements.com To: linux-kernel@vger.kernel.org Cc: coreboot@coreboot.org, patrick.rudolph@9elements.com, Arthur Heymans , Greg Kroah-Hartman , Thomas Gleixner , Allison Randal , Alexios Zavras Subject: [PATCH 3/3] firmware: google: Probe for a GSMI handler in firmware Date: Fri, 15 Nov 2019 14:48:39 +0100 Message-Id: <20191115134842.17013-4-patrick.rudolph@9elements.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20191115134842.17013-1-patrick.rudolph@9elements.com> References: <20191115134842.17013-1-patrick.rudolph@9elements.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arthur Heymans Currently this driver is loaded if the DMI string matches coreboot and has a proper smi_command in the ACPI FADT table, but a GSMI handler in SMM is an optional feature in coreboot. So probe for a SMM GSMI handler before initializing the driver. If the smihandler leaves the calling argument in %eax in the SMM save state untouched that generally means the is no handler for GSMI. Signed-off-by: Arthur Heymans --- drivers/firmware/google/gsmi.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c index 974c769b75cf..a3eaa9f41125 100644 --- a/drivers/firmware/google/gsmi.c +++ b/drivers/firmware/google/gsmi.c @@ -746,6 +746,7 @@ MODULE_DEVICE_TABLE(dmi, gsmi_dmi_table); static __init int gsmi_system_valid(void) { u32 hash; + u16 cmd, result; if (!dmi_check_system(gsmi_dmi_table)) return -ENODEV; @@ -780,6 +781,23 @@ static __init int gsmi_system_valid(void) return -ENODEV; } + /* Test the smihandler with a bogus command. If it leaves the + * calling argument in %ax untouched, there is no handler for + * GSMI commands. + */ + cmd = GSMI_CALLBACK | 0xff << 8; + asm volatile ( + "outb %%al, %%dx\n\t" + : "=a" (result) + : "0" (cmd), + "d" (acpi_gbl_FADT.smi_command) + : "memory", "cc" + ); + if (cmd == result) { + pr_info("gsmi: no gsmi handler in firmware\n"); + return -ENODEV; + } + /* Found */ return 0; } -- 2.21.0