From: 'Mika Westerberg' > Sent: 08 August 2019 10:58 > On Wed, Aug 07, 2019 at 04:41:30PM +0000, David Laight wrote: > > From: 'Mika Westerberg' [mailto:mika.westerberg@xxxxxxxxxxxxxxx] > > > Sent: 07 August 2019 17:36 > > > > > > On Wed, Aug 07, 2019 at 04:22:26PM +0000, David Laight wrote: > > > > From: Mika Westerberg > > > > > Sent: 07 August 2019 17:14 > > > > > To: David Laight > > > > > > > > > > On Fri, Jul 05, 2019 at 04:04:19PM +0000, David Laight wrote: > > > > > > > Really a matter of taste, but maybe you want to consider having a single > > > > > > > function, with a 3rd parameter, bool is_tx. > > > > > > > The calls here will be unified to: > > > > > > > ring_iowrite(ring, ring->head, ring->is_tx); > > > > > > > (No condition is needed here). > > > > > > > > > > > > > > The implementation uses the new parameter to decide which part of the register > > > > > > > to mask, reducing the code duplication (in my eyes): > > > > > > > > > > > > > > val = ioread32(ring_desc_base(ring) + 8); > > > > > > > if (is_tx) { > > > > > > > val &= 0x0000ffff; > > > > > > > val |= value << 16; > > > > > > > } else { > > > > > > > val &= 0xffff0000; > > > > > > > val |= value; > > > > > > > } > > > > > > > iowrite32(val, ring_desc_base(ring) + 8); > > > > > > > > > > > > > > I'm not sure if it improves the readability or makes it worse. Your call. > > > > > > > > > > > > Gah, that is all horrid beyond belief. > > > > > > If a 32bit write is valid then the hardware must not be updating > > > > > > the other 16 bits. > > > > > > In which case the driver knows what they should be. > > > > > > So it can do a single 32bit write of the required value. > > > > > > > > > > I'm not entirely sure I understand what you say above. Can you shed some > > > > > light on this by a concrete example how it should look like? :-) > > > > > > > > The driver must know both the tx and rx ring values, so: > > > > iowrite32(tx_val << 16 | rx_val, ring_desc_base(ring) + 8); > > > > > > > > > > I see. However, prod or cons side gets updated by the hardware as it > > > processes buffers and other side is only updated by the driver. I'm not > > > sure the above works here. > > > > If the hardware updates the other half of the 32bit word it doesn't ever work. > > > > In that case you must do 16bit writes. > > If the hardware is ignoring the byte-enables it is broken and unusable. > > It is quite usable as I'm running this code on real hardware ;-) but > 32-bit access is needed. > > The low or high 16-bits are read-only depending on the ring (Tx or Rx) > and updated by the hardware. It ignores writes to that part so we could > do this for Tx ring: > > iowrite32(prod << 16, ring_desc_base(ring) + 8); > > and this for Rx ring: > > iowrite32(cons, ring_desc_base(ring) + 8); > > Do you see any issues with this? No, just comment that the hardware ignores the write to the other bytes. You probably want separate functions - to remove the mispredicted branch. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
