Hi, On Mon, Jul 31, 2017 at 05:59:59PM -0700, Palmer Dabbelt wrote: > This patch adds a driver for the Platform Level Interrupt Controller > (PLIC) specified as part of the RISC-V supervisor level ISA manual. > The PLIC connocts global interrupt sources to the local interrupt s/connocts/connects/ > controller on each hart. A PLIC is present on all RISC-V systems. > > Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxx> > --- [...] > +/* > + * From the RISC-V Privlidged Spec v1.10: > + * > + * Global interrupt sources are assigned small unsigned integer identifiers, > + * beginning at the value 1. An interrupt ID of 0 is reserved to mean “no > + * interrupt”. Interrupt identifiers are also used to break ties when two or > + * more interrupt sources have the same assigned priority. Smaller values of > + * interrupt ID take precedence over larger values of interrupt ID. > + * > + * While the RISC-V supervisor spec doesn't define the maximum number of > + * devices supported by the PLIC, the largest number supported by devices > + * marked as 'riscv,plic0' (which is the only device type this driver supports, > + * and is the only extant PLIC as of now) is 1024. As mentioned above, device > + * 0 is defined to be non-existant so this device really only supports 1023 > + * devices. > + */ > +#define MAX_DEVICES 1024 > +#define MAX_CONTEXTS 15872 How do you derive 15872 as the value of MAX_CONTEXTS? > + > +/* > + * The PLIC consists of memory-mapped control registers, with a memory map as > + * follows: > + * > + * base + 0x000000: Reserved (interrupt source 0 does not exist) > + * base + 0x000004: Interrupt source 1 priority > + * base + 0x000008: Interrupt source 2 priority > + * ... > + * base + 0x000FFC: Interrupt source 1023 priority > + * base + 0x001000: Pending 0 > + * base + 0x001FFF: Pending "Pending"? > + * base + 0x002000: Enable bits for sources 0-31 on context 0 > + * base + 0x002004: Enable bits for sources 32-63 on context 0 > + * ... > + * base + 0x0020FC: Enable bits for sources 992-1023 on context 0 > + * base + 0x002080: Enable bits for sources 0-31 on context 1 This seems to overlap. Are more than 512 sources per context actually possible? > + * ... > + * base + 0x002100: Enable bits for sources 0-31 on context 2 > + * ... > + * base + 0x1F1F80: Enable bits for sources 992-1023 on context 15871 > + * base + 0x1F1F84: Reserved > + * ... (higher context IDs would fit here, but wouldn't fit > + * inside the per-context priority vector) > + * base + 0x1FFFFC: Reserved > + * base + 0x200000: Priority threshold for context 0 > + * base + 0x200004: Claim/complete for context 0 > + * base + 0x200008: Reserved > + * ... > + * base + 0x200FFC: Reserved > + * base + 0x201000: Priority threshold for context 1 > + * base + 0x201004: Claim/complete for context 1 > + * ... > + * base + 0xFFE000: Priority threshold for context 15871 > + * base + 0xFFE004: Claim/complete for context 15871 > + * base + 0xFFF008: Reserved 0xFFE004 and 0xFFF008 are 0x1004 bytes apart. Is 0xFFF008 a typo? > + * ... > + * base + 0xFFFFFC: Reserved As far as I can see, given that the Priority threshold/Claim/complete area begins at base+0x200000 and ends at base+0x1000000 (exclusive), and the space occupied by one context is 0x1000 bytes, there should be space for (0x1000000-0x200000)/0x1000 = 0xe00 = 3584, not 15872 contexts. Am I missing something? Jonathan Neuschäfer
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