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[78.94.0.50]) by smtp.gmail.com with ESMTPSA id z14sm21700530wrl.60.2019.11.18.00.39.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Nov 2019 00:39:24 -0800 (PST) From: patrick.rudolph@9elements.com To: linux-kernel@vger.kernel.org Cc: coreboot@coreboot.org, Arthur Heymans , Patrick Rudolph , Thomas Gleixner , Allison Randal , Alexios Zavras , Greg Kroah-Hartman Subject: [Patch v2 3/3] firmware: google: Probe for a GSMI handler in firmware Date: Mon, 18 Nov 2019 09:39:00 +0100 Message-Id: <20191118083903.19311-3-patrick.rudolph@9elements.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20191118083903.19311-1-patrick.rudolph@9elements.com> References: <20191118083903.19311-1-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 Signed-off-by: Patrick Rudolph --- drivers/firmware/google/gsmi.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c index 974c769b75cf..5b2011ebbe26 100644 --- a/drivers/firmware/google/gsmi.c +++ b/drivers/firmware/google/gsmi.c @@ -76,6 +76,7 @@ #define GSMI_CMD_LOG_S0IX_RESUME 0x0b #define GSMI_CMD_CLEAR_CONFIG 0x20 #define GSMI_CMD_HANDSHAKE_TYPE 0xC1 +#define GSMI_CMD_RESERVED 0xff /* Magic entry type for kernel events */ #define GSMI_LOG_ENTRY_TYPE_KERNEL 0xDEAD @@ -746,6 +747,7 @@ 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 +782,23 @@ 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 | GSMI_CMD_RESERVED << 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