Re: pci_size() error condition
On Thu, Jul 14, 2005 at 11:04:00AM -0500, John Rose wrote: > Okay, point taken :) So for cases of base == maxbase, why would we ever > want to return a nonzero value? What is the intended purpose of the > second part of that conditional? Well, just two examples (both for PCI IO limited to 16 bits for simplicity, but still from real life): 1. Consider some BAR that defines 16 bytes of IO space. It's perfectly valid for the PCI firmware to program this BAR to its max value, so after writing all 1s during the probe and proper masking we have base == maxbase == 0xfff0. But, since all high order bits are all 1s, (((base | size) & mask) != mask) is false, and we return correct value of 16. 2. Another BAR of some broken PCI device (typically, IDE controller) has *read-only* value of 0x1f0, for instance. After writing 0x we still read back the same 0x1f0, so base == maxbase == 0x1f0. But the second part of that "if" clause is now true, so we return 0, which means that the BAR is invalid and must be ignored. Ivan. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: pci_size() error condition
> It was always effectual for IO where the mask is 0x. Okay, point taken :) So for cases of base == maxbase, why would we ever want to return a nonzero value? What is the intended purpose of the second part of that conditional? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: pci_size() error condition
It was always effectual for IO where the mask is 0x. Okay, point taken :) So for cases of base == maxbase, why would we ever want to return a nonzero value? What is the intended purpose of the second part of that conditional? - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: pci_size() error condition
On Thu, Jul 14, 2005 at 11:04:00AM -0500, John Rose wrote: Okay, point taken :) So for cases of base == maxbase, why would we ever want to return a nonzero value? What is the intended purpose of the second part of that conditional? Well, just two examples (both for PCI IO limited to 16 bits for simplicity, but still from real life): 1. Consider some BAR that defines 16 bytes of IO space. It's perfectly valid for the PCI firmware to program this BAR to its max value, so after writing all 1s during the probe and proper masking we have base == maxbase == 0xfff0. But, since all high order bits are all 1s, (((base | size) mask) != mask) is false, and we return correct value of 16. 2. Another BAR of some broken PCI device (typically, IDE controller) has *read-only* value of 0x1f0, for instance. After writing 0x we still read back the same 0x1f0, so base == maxbase == 0x1f0. But the second part of that if clause is now true, so we return 0, which means that the BAR is invalid and must be ignored. Ivan. - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: pci_size() error condition
On Wed, Jul 13, 2005 at 05:53:13PM -0500, John Rose wrote: > Before a recent change, mask was a 64-bit number. The second part of > the if statement would always resolve to true, since the 32-bit bitop > would never equal the 64-bit mask. So the second part of the if > statement was ineffectual up until very recently. It was always effectual for IO where the mask is 0x. Ivan. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
pci_size() error condition
Can anyone lend an explanation of the following?
/* base == maxbase can be valid only if the BAR has
already been programmed with all 1s. */
if (base == maxbase && ((base | size) & mask) != mask) {
printk("%s: 2 returning 0\n", __FUNCTION__);
return 0;
}
Before a recent change, mask was a 64-bit number. The second part of
the if statement would always resolve to true, since the 32-bit bitop
would never equal the 64-bit mask. So the second part of the if
statement was ineffectual up until very recently.
After the recent change, this is no longer the case. Nonzero PCI sizes
are generating bogus resource records for some PPC64 devices. So for
cases of base == maxbase, why would we ever want to return a nonzero
value? What is the intended purpose of the second part of that
conditional?
Thanks-
John
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
pci_size() error condition
Can anyone lend an explanation of the following?
/* base == maxbase can be valid only if the BAR has
already been programmed with all 1s. */
if (base == maxbase ((base | size) mask) != mask) {
printk(%s: 2 returning 0\n, __FUNCTION__);
return 0;
}
Before a recent change, mask was a 64-bit number. The second part of
the if statement would always resolve to true, since the 32-bit bitop
would never equal the 64-bit mask. So the second part of the if
statement was ineffectual up until very recently.
After the recent change, this is no longer the case. Nonzero PCI sizes
are generating bogus resource records for some PPC64 devices. So for
cases of base == maxbase, why would we ever want to return a nonzero
value? What is the intended purpose of the second part of that
conditional?
Thanks-
John
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: pci_size() error condition
On Wed, Jul 13, 2005 at 05:53:13PM -0500, John Rose wrote: Before a recent change, mask was a 64-bit number. The second part of the if statement would always resolve to true, since the 32-bit bitop would never equal the 64-bit mask. So the second part of the if statement was ineffectual up until very recently. It was always effectual for IO where the mask is 0x. Ivan. - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
