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fm10k/base: document ITR scale workaround

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Add comments which properly explain the undocumented use of bits in
TDLEN register prior to VF initializing it to the correct value. Note
that the mechanism is entirely software-defined and explain its purpose
to help reduce confusion in the future.

Signed-off-by: Wang Xiao W <xiao.w.wang@intel.com>
Tested-by: Heng Ding <hengx.ding@intel.com>
Acked-by: Jing Chen <jing.d.chen@intel.com>
This commit is contained in:
Xiao Wang 2016-02-19 19:06:53 +08:00 committed by Thomas Monjalon
parent 360c4545e0
commit a177f52f90
3 changed files with 23 additions and 1 deletions
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6
drivers/net/fm10k/base/fm10k_pf.c
View File

@ -958,7 +958,8 @@ STATIC s32 fm10k_iov_assign_default_mac_vlan_pf(struct fm10k_hw *hw,
FM10K_WRITE_REG(hw, FM10K_TDBAH(vf_q_idx), tdbah);
/* Provide the VF the ITR scale, using software-defined fields in TDLEN
* to pass the information during VF initialization
* to pass the information during VF initialization. See definition of
* FM10K_TDLEN_ITR_SCALE_SHIFT for more details.
*/
FM10K_WRITE_REG(hw, FM10K_TDLEN(vf_q_idx), hw->mac.itr_scale <<
FM10K_TDLEN_ITR_SCALE_SHIFT);
@ -1095,6 +1096,9 @@ STATIC s32 fm10k_iov_reset_resources_pf(struct fm10k_hw *hw,
for (i = queues_per_pool; i--;) {
FM10K_WRITE_REG(hw, FM10K_TDBAL(vf_q_idx + i), tdbal);
FM10K_WRITE_REG(hw, FM10K_TDBAH(vf_q_idx + i), tdbah);
/* See definition of FM10K_TDLEN_ITR_SCALE_SHIFT for an
* explanation of how TDLEN is used.
*/
FM10K_WRITE_REG(hw, FM10K_TDLEN(vf_q_idx + i),
hw->mac.itr_scale <<
FM10K_TDLEN_ITR_SCALE_SHIFT);

9
drivers/net/fm10k/base/fm10k_type.h
View File

@ -350,6 +350,15 @@ struct fm10k_hw;
#define FM10K_TDBAL(_n) ((0x40 * (_n)) + 0x8000)
#define FM10K_TDBAH(_n) ((0x40 * (_n)) + 0x8001)
#define FM10K_TDLEN(_n) ((0x40 * (_n)) + 0x8002)
/* When fist initialized, VFs need to know the Interrupt Throttle Rate (ITR)
* scale which is based on the PCIe speed but the speed information in the PCI
* configuration space may not be accurate. The PF already knows the ITR scale
* but there is no defined method to pass that information from the PF to the
* VF. This is accomplished during VF initialization by temporarily co-opting
* the yet-to-be-used TDLEN register to have the PF store the ITR shift for
* the VF to retrieve before the VF needs to use the TDLEN register for its
* intended purpose, i.e. before the Tx resources are allocated.
*/
#define FM10K_TDLEN_ITR_SCALE_SHIFT 9
#define FM10K_TDLEN_ITR_SCALE_MASK 0x00000E00
#define FM10K_TDLEN_ITR_SCALE_GEN1 2

9
drivers/net/fm10k/base/fm10k_vf.c
View File

@ -74,6 +74,11 @@ STATIC s32 fm10k_stop_hw_vf(struct fm10k_hw *hw)
FM10K_WRITE_REG(hw, FM10K_TDBAH(i), bah);
FM10K_WRITE_REG(hw, FM10K_RDBAL(i), bal);
FM10K_WRITE_REG(hw, FM10K_RDBAH(i), bah);
/* Restore ITR scale in software-defined mechanism in TDLEN
* for next VF initialization. See definition of
* FM10K_TDLEN_ITR_SCALE_SHIFT for more details on the use of
* TDLEN here.
*/
FM10K_WRITE_REG(hw, FM10K_TDLEN(i), tdlen);
}
@ -157,6 +162,10 @@ STATIC s32 fm10k_init_hw_vf(struct fm10k_hw *hw)
/* fetch default VLAN and ITR scale */
hw->mac.default_vid = (FM10K_READ_REG(hw, FM10K_TXQCTL(0)) &
FM10K_TXQCTL_VID_MASK) >> FM10K_TXQCTL_VID_SHIFT;
/* Read the ITR scale from TDLEN. See the definition of
* FM10K_TDLEN_ITR_SCALE_SHIFT for more information about how TDLEN is
* used here.
*/
hw->mac.itr_scale = (FM10K_READ_REG(hw, FM10K_TDLEN(0)) &
FM10K_TDLEN_ITR_SCALE_MASK) >>
FM10K_TDLEN_ITR_SCALE_SHIFT;