> -----Original Message----- > From: Darren Hart [mailto:dvhart@xxxxxxxxxxxxx] > Sent: Friday, June 8, 2018 8:04 PM > To: Andy Shevchenko > Cc: Stuart Hayes; Warzecha, Douglas; Limonciello, Mario; Dominguez, Jared; Linux > Kernel Mailing List; Platform Driver > Subject: Re: [PATCH resend v2] dcdbas: Add support for WSMT ACPI table > > On Thu, Jun 07, 2018 at 08:11:41PM +0300, Andy Shevchenko wrote: > > On Thu, Jun 7, 2018 at 6:59 PM, Stuart Hayes <stuart.w.hayes@xxxxxxxxx> > wrote: > > > If the WSMT ACPI table is present and indicates that a fixed communication > > > buffer should be used, use the firmware-specified buffer instead of > > > allocating a buffer in memory for communications between the dcdbas driver > > > and firmare. > > > > > config DCDBAS > > > tristate "Dell Systems Management Base Driver" > > > - depends on X86 > > > + depends on X86 && ACPI > > > > > > Hmm... I'm not sure about this dependency. > > So, the question is do all users actually need this? How did it work > > previously? How has this been tested in case when command line has > > "acpi=off" (yes, this one just for sake of test, I don't believe it's > > a real use case)? > > Yeah... after the 4.16 and 4.17 KConfig fumbling around the SMBIOS > driver which intersected with this one.... this needs to be thoroughly > covered, tested, and thought through. Linus was.... generous in the > number of attempts it took us to get that right. > > Did DCDBAS ever work on a system without ACPI? Yes, I would expect it would have functioned on a system with kernel's ACPI disabled. However I also agree this isn't a real use case with a modern Machine. Perhaps the right thing to do is #ifdef CONFIG_ACPI For the WSMT relevant items in this patch? > > > > > > #include <linux/string.h> > > > #include <linux/types.h> > > > #include <linux/mutex.h> > > > +#include <linux/acpi.h> > > > > Please, try to keep an order as much as possible. > > For example, in given context this line should be before string.h (I > > didn't check the actual file, perhaps even upper). > > > > > #include <asm/io.h> > > > > > > #include "dcdbas.h" > > > > > /* Calling Interface SMI */ > > > - smi_cmd->ebx = (u32) virt_to_phys(smi_cmd->command_buffer); > > > + smi_cmd->ebx = smi_data_buf_phys_addr > > > + + offsetof(struct smi_cmd, command_buffer); > > > > Please, keep at least + on the previous line. > > Also, I'm not sure what is the difference now. Especially for previous > > users when this wasn't the part of the driver. > > Some explanation needed. > > > > > +static u8 checksum(u8 *buffer, u8 length) > > > +{ > > > + u8 sum = 0; > > > + u8 *end = buffer + length; > > > + > > > + while (buffer < end) > > > + sum = (u8)(sum + *(buffer++)); > > > > Why not simple > > > > sum += *buffer++; > > > > ? > > > > > + return sum; > > > +} > > > > And I would rather check if we have similar algoritms already in the > > kernel which we might re-use. > > Seems to be some options in lib/checksum.c to check. > > > > > > + > > > +static inline struct smm_eps_table *check_eps_table(u8 *addr) > > > +{ > > > + struct smm_eps_table *eps = (struct smm_eps_table *)addr; > > > + > > > > > + if (strncmp(SMM_EPS_SIG, eps->smm_comm_buff_anchor, 4) != 0) > > > > I'm not sure about strings operation here. > > I would rather do like with other magic constants: introduce hex value > > and compare it as unsigned integer. > > > > Also, it might be a warning, since \0 wasn't ever checked from the > > string literal. Though, I'm not sure if it applicable to strncmp() > > function (it's for strncpy for sure). > > I think we're OK here, and we're being consistent with the > dell-wmi-descriptor test for "DELL WMI". I don't recall if it was that > one or something else, but doing it in HEX ended up being more > confusing. The \0 isn't an issue since strncmp will only compare the n > (4) bytes. > > > > > > + return NULL; > > > + > > > + if (checksum(addr, eps->length) != 0) > > > + return NULL; > > > + > > > + return eps; > > > +} > > > + > > > +static int dcdbas_check_wsmt(void) > > > +{ > > > + struct acpi_table_wsmt *wsmt = NULL; > > > + struct smm_eps_table *eps = NULL; > > > + u8 *addr; > > > + > > > + acpi_get_table(ACPI_SIG_WSMT, 0, (struct acpi_table_header **)&wsmt); > > > + if (!wsmt) > > > + return 0; > > > + > > > + /* Check if WSMT ACPI table shows that protection is enabled */ > > > + if (!(wsmt->protection_flags & ACPI_WSMT_FIXED_COMM_BUFFERS) > > > + || !(wsmt->protection_flags > > > + & ACPI_WSMT_COMM_BUFFER_NESTED_PTR_PROTECTION)) > > > + return 0; > > > + > > > + /* Scan for EPS (entry point structure) */ > > > + for (addr = (u8 *)__va(0xf0000); > > > + addr < (u8 *)__va(0x100000 - sizeof(struct smm_eps_table)) && !eps; > > > > Perhaps better to do > > > > for (...) { > > eps = ...(); > > if (eps) > > break; > > } > > > > Also I've a feeling that 0xf0000 constant is defined already somewhere > > under arch/x86/include/asm or evem include/linux. > > But... is it defined for this purpose? If not, I'd prefer it hardcoded > (or with a DEFINE). > > > > > > + addr += 1) > > > > += 1?! > > All tables I saw in BIOS are aligned with 16 bytes. Is it the case here? > > > > Is there any other means to check if the table present? ACPI code? > > Method / variable? > > > > > + eps = check_eps_table(addr); > > > + > > > + if (!eps) { > > > + dev_dbg(&dcdbas_pdev->dev, "found WSMT, but no EPS found\n"); > > > + return -ENODEV; > > > + } > > > + > > > + /* > > > + * Get physical address of buffer and map to virtual address. > > > + * Table gives size in 4K pages, regardless of actual system page size. > > > + */ > > > > > + if (eps->smm_comm_buff_addr + 8 > U32_MAX) { > > > > if (upper_32_bits(..._addr + 8)) { > > > > ? > > > > > + dev_warn(&dcdbas_pdev->dev, "found WSMT, but EPS buffer address > is above 4GB\n"); > > > + return -EINVAL; > > > + } > > > + eps_buffer = (u8 *)memremap(eps->smm_comm_buff_addr, > > > > Why casting? > > > > > + eps->num_of_4k_pages * 4096, MEMREMAP_WB); > > > > This multiplication looks strange. Perhaps use PAGE_SIZE? > > > > > + if (!eps_buffer) { > > > + dev_warn(&dcdbas_pdev->dev, "found WSMT, but failed to map EPS > buffer\n"); > > > + return -ENOMEM; > > > + } > > > + > > > + /* First 8 bytes of buffer is for semaphore */ > > > + smi_data_buf_phys_addr = (u32) eps->smm_comm_buff_addr + 8; > > > > lower_32_bits() ? > > > > > + smi_data_buf = eps_buffer + 8; > > > > > + smi_data_buf_size = (unsigned long) min(eps->num_of_4k_pages * 4096 - > 8, > > > + (u64) ULONG_MAX); > > > > This is too twisted code. First, it needs explanation. > > Second, it might need some refactoring. > > > > (Yes, I got the idea, but would it be better implementation?) > > > > > + max_smi_data_buf_size = smi_data_buf_size; > > > + wsmt_enabled = true; > > > + dev_info(&dcdbas_pdev->dev, > > > + "WSMT found, using firmware-provided SMI buffer.\n"); > > > + return 1; > > > +} > > > > > #define SMI_CMD_MAGIC (0x534D4931) > > > > > > +#define SMM_EPS_SIG "$SCB" > > > > Just integer like above and put the sting as a comment. > > (Side note: above magic also looks like string) > > Given the above, I think we can use the more recognizable string - since > that is clearly how they think of this label. > > Otherwise, agree with a follow-up to all of Andy's feedback. > > -- > Darren Hart > VMware Open Source Technology Center
