Subject: Re: imx6 and keystone PCIe abort handling

From: Russell King - ARM Linux admin <[email-masked]>
Date: Fri, 13 Dec 2019 00:51:09 +0000

On Thu, Dec 12, 2019 at 06:32:36PM -0600, Bjorn Helgaas wrote:
> Hi folks,
> 
> Why are ks_pcie_fault() and imx6q_pcie_abort_handler() different?  I
> think they're doing the same thing, and the "instr & 0x0e100090" part
> is the same, but only imx6 has the "instr & 0x0c100000" part.  And the
> return values are different in some cases.

Here's the opcodes for the three different types of loads that would
be interesting.

   0:   e5910000        ldr     r0, [r1] ; 32-bit
   4:   e5d10000        ldrb    r0, [r1] ; 8-bit
   8:   e1d100b0        ldrh    r0, [r1] ; 16-bit

So, (instr & 0x0e100090) == 0x00100090 is trie for the ldrh case.
(instr & 0x0c100000) == 0x04100000 is true for the ldr and ldrb case.

So, the keystone version only traps ldrh instructions, whereas the
imx6 traps them all.

> Could/should these be shared somehow?  They're both under #ifdef
> CONFIG_ARM, so maybe it could be provided by arch/arm?
> 
>   static int ks_pcie_fault(unsigned long addr, unsigned int fsr,
> 			   struct pt_regs *regs)
>   {
> 	  unsigned long instr = *(unsigned long *) instruction_pointer(regs);
> 
> 	  if ((instr & 0x0e100090) == 0x00100090) {
> 		  int reg = (instr >> 12) & 15;
> 
> 		  regs->uregs[reg] = -1;
> 		  regs->ARM_pc += 4;
> 	  }
> 
> 	  return 0;
>   }
> 
>   static int imx6q_pcie_abort_handler(unsigned long addr,
> 		  unsigned int fsr, struct pt_regs *regs)
>   {
> 	  unsigned long pc = instruction_pointer(regs);
> 	  unsigned long instr = *(unsigned long *)pc;
> 	  int reg = (instr >> 12) & 15;
> 
> 	  /*
> 	   * If the instruction being executed was a read,
> 	   * make it look like it read all-ones.
> 	   */
> 	  if ((instr & 0x0c100000) == 0x04100000) {
> 		  unsigned long val;
> 
> 		  if (instr & 0x00400000)
> 			  val = 255;
> 		  else
> 			  val = -1;
> 
> 		  regs->uregs[reg] = val;
> 		  regs->ARM_pc += 4;
> 		  return 0;
> 	  }
> 
> 	  if ((instr & 0x0e100090) == 0x00100090) {
> 		  regs->uregs[reg] = -1;
> 		  regs->ARM_pc += 4;
> 		  return 0;
> 	  }
> 
> 	  return 1;
>   }
> 
> 

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